Kleiman's greatest success was with the golden lion tamarin, a small, reddish-orange monkey that inhabits Brazil's coastal forest. In the early 1970s she responded to an emergency alert from Brazilian biologist Adelmar Coimbra Filho, who reported that the tamarin population was down to several hundred in the wild and only 75 in captivity. Kleiman worked with Filho to convince more than a dozen zoos to engage in a cooperative lending program to foster breeding.