Two satellite DNAs, designated CapA and CapB, were isolated from the neotropical primate, Cebus apella. The satellites exhibit nonoverlapping distributions on C. apella chromosomes. CapA is a major component of interstitial regions of constitutive heterochromatin, a very large block of heterochromatin comprising most of the long arm of chromosome 11, and some telomeres. The CapA monomer has a length of about 1500 bp and appears recently to have undergone an amplification episode in the C. apella genome. CapA-like sequences are probably present in members of the family Cebidae (to which C. apella belongs), but not in members of the family Callitrichidae (marmosets). CapB sequences can be detected at the centromeres of many C. apella chromosomes, and similar sequences are present in all neotropical primates. The 342 bp CapB monomer shares 60%-64% sequence identity with several alpha satellite sequences of human origin. Because of its structure, sequence, and location, it appears that CapB is the New World primate homolog of Old World primate alpha satellite DNA.