BUENOS AIRES -- Their disappearance is one of Argentina's most enduring mysteries. In 1810, black residents accounted for about 30 percent of the population of Buenos Aires. By 1887, however, their numbers had plummeted to 1.8 percent.

So where did they go? The answer, it turns out, is nowhere.

Popular myth has offered two historical hypotheses: a yellow fever epidemic in 1871 that devastated black urban neighborhoods, and a brutal war with Paraguay in the 1860s that put many black Argentines on the front lines.

But two new studies are challenging those old notions, using distinct methods: a door-to-door census to determine how many Argentines consider themselves black, and an analysis of DNA samples to detect traces of African ancestry in those who consider themselves white.

The results are only partially compiled, but they suggest that many of the black Argentines did not vanish; they just faded into the mixed-race populace and became lost to demography. According to some researchers, as many as 10 percent of Buenos Aires residents are partly descended from black Argentines but have no idea.

"People for years have accepted the idea that there are no black people in Argentina," said Miriam Gomes, a professor of literature at the University of Buenos Aires who is part black and considers herself Afro-Argentine. "Even the schoolbooks here accepted this as a fact. But where did that leave me?"

It left her as part of a practically invisible fringe, a group whose very existence had been snubbed by the country's early statesmen. The nation aggressively courted "the reviving spirit of European civilization" -- in the words of 19th-century Argentine social architect Juan Bautista Alberdi -- and promoted an image of a European country transplanted on South American soil.

"Argentina was interested in presenting itself as a white country," said George Reid Andrews, a history professor at the University of Pittsburgh who has specialized in black history in Latin America. "Its ideologues and writers put a great emphasis on the yellow fever epidemic and the war, and it was feasible to pretend that the black population had simply disappeared as immigration exploded."

Estimates of the current population of blacks in Buenos Aires are essentially wild guesses, partly because the Argentine government has not reflected African racial ancestry in its census counts in well over a century.

But Gomes is among the group of scholars and scientists who want to take a closer look at today's black culture in Argentina, which they believe will help them form a clearer picture of what happened in the past.

Funded in part by the World Bank and assisted by Argentina's census bureau, the group launched a limited census of various neighborhoods in the capital last month.

First, they asked whether any people in the house considered themselves Afro-Argentine, then they asked whether anyone in the house had any black ancestors. In neighborhoods with historically high concentrations of black residents, they conducted more detailed surveys of religious practice, diet and social organization -- an attempt to measure the influence of African culture there.

The results won't be analyzed until later this year. Diego Masello, a professor with the National University of the Third of February, said the thorniest challenge of the census has been eliciting honest answers -- or any answers at all.

"In some cases, the census-takers reported that residents who visibly had some African traits, even some who appeared completely black, absolutely refused to participate," said Masello, who is helping direct the census.

Gomes said such responses have been frustrating, but illustrative.

"Without a doubt, racial prejudice is great in this society, and people want to believe that they are white," Gomes said. "Here, if someone has one drop of white blood, they call themselves white."

But personal definitions do not count when analyzing DNA, which is what a group of scientists from the University of Buenos Aires and Oxford University in England did earlier this year. After collecting blood samples at a local hospital, they searched for genetic markers that indicate African ancestry. The results, to be published this year in the American Journal of Physical Anthropology, suggested that 10 percent of those who identified themselves as white were, in part, descendants of black Argentines.

"A lot of people were very surprised by this," said Francisco R. Carnese, a geneticist at the University of Buenos Aires and co-author of the study. "When you walk around Buenos Aires, you don't see signs of African ancestry. But you see it in the genes."

Carnese said there was also a growing desire among Argentines to figure out their heritage -- one reason that multiple studies are trying to shed light on the same thing, he said. For most Argentines, that means delving into the cultures of Italy, England and Germany, but Africa also deserves consideration, he said.

The near-invisibility of black culture and roots in Argentina has been a striking contrast with neighboring Brazil, which once imported millions of African slaves and has a large, high-profile Afro-Brazilian community.

Africans had a strong hand in shaping Brazilian culture: samba music, the Lenten festival of carnival and African religions that have melded with Roman Catholicism to form hybrid systems of faith. Even the national dish, a black bean staple called feijoada , is popularly credited to 16th-century slaves.

In Argentina, partly in response to the new research, black interest groups have started promoting what they say is a strong African influence on some of the traditions most closely associated with Argentina. There was little slave trade with Argentina; many Africans who ended up there had originally been imported to Brazil.

"The first paintings of people dancing the tango are of people of African descent," Gomes said.

The asado -- the traditional Argentine barbecue that includes glands, livers and other organs from cows -- also was influenced by blacks who collected the parts that the Argentine cowboys, or gauchos, threw away, according to Masello.

The census-takers hope their work will inspire the government to include African ancestry in its next census in 2011 -- a decision that Gomes said she believed would go a long way in acknowledging the role of Africa in today's Argentina.

"If we're not counted," she said, "there's no way to really convince people that we actually exist."