Over 90% of the Atlantic forest in Brazil has been lost to logging, development and cultivation. The species is also vulnerable to fire and hunting (4). Areas of prime habitat occur in and around the Morro do Diabo State Park; however, 5% of this area was flooded in the early 1980's, following the construction of a hydroelectric plant (7). The remaining black lion tamarin populations have been isolated for some time, and studies have shown that genetic diversity is extremely low as a result of inbreeding (7). Inbreeding depression, which can reduce the fitness of the population in terms of survival, reproductive capacity and growth, is therefore a cause for concern in this species.