One hundred and forty-three sakis (Pithecia), 107 bearded sakis (Chiropotes), and 7 red uakaris (Cacajao) were studied in relation to 18 genetic loci expressed on blood through electrophoretic techniques. Eight of the 18 loci showed intrapopulational variation. The low level of genetic diversity found in Pithecia could be a consequence of a decrease in populational size due to intense habitat destruction. The genetic distances between the species investigated were:Pithecia ×Chiropotes: 0.49;Pithecia ×Cacajao: 0.57;Cacajao ×Chiropotes: 0.18-0.20. These results suggest, in accordance with other data, that Chiropotes and Cacajao constitute a sister group within the pithecines. © 1995 Japan Monkey Centre.