This research will investigate genetic divergence and phylogenetic relationships among species of the owl monkey, Aotus. Owl monkeys are widely distributed in Central and South America. Until ten years ago it was generally assumed that owl monkeys comprised a single species, A. trivirgatus. More recently, however, it has been suggested that the owl monkey represents at least ten allopatric species which have distinct geographic distributions and can be distinguished both phenotypically and genotypically. Aotus has undergone an extraordinary amount of karyotypic change with diploid chromosome counts ranging from 46 to 58, but changes in other genetic characters have not yet been investigated. This research will examine mitochondrial DNA (mtDNA) and several related gene sequences within and among several karyotypically distinct species. This work is important because of the use of the owl monkey as a model for malarial research, and because of the unusual nature of chromosomal rearrangements in this genus.