With the sakis (Pithecia) and the bearded sakis (Chiropotes), the uakaris (Cacajao) constitute the cebid subfamily, Pitheciinae. The most recent revision recognized six Cacajao subspecies in two species, confined to the Amazon basin. Before 1970 most field information derived from 19th century travellers. Studies still lag behind those of other cebid genera. This paper summarises the known ecology of Cacajao, and identifies future research and conservation priorities. The relevance of Pleistocene refugia and metachromism in analysing its biogeography is discussed. Range size remains obscure but, with the exception of C. c. calvus, may be extensive, as all other subspecies appear to migrate in the dry season from flooded riverine forest to terra firme. Observed group size ranges from 5 to 50, indicating the operation of a fission-fusion society. Social organization appears to be multi-male and non-hierarchical. This accords with the minimal sexual dimorphism. The highly developed canines function primarily as fruit openers. Cacajao is a dietary specialist on hard-shelled fruit, and appears unique among Amazonian cebids in its dependence (at least seasonally) on riverine forests. Hunting may be a problem locally, but local taboos sometimes offer protection. They appear vulnerable to habitat disturbance. On the Rio Negro, the range of C. m. melanocephalus appears to have greatly diminished. To ensure protection of viable populations, the inferred dietary dependence on seasonal migration may require accommodation. Research priorities include the status, habitat preference, diet and social ecology of all taxa except C. c. calvus. A more complete knowledge of the biogeography of the genus would be valuable.Copyright © 1997 S. Karger AG, Basel