Although data on nucleotide sequence variation in the human nuclear genome have begun to accumulate, little is known about genomic diversity in chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). A 10,154-base pair sequence on the chimpanzee X chromosome is reported, representing all major subspecies and bonobos. Comparison to humans shows the diversity of the chimpanzee sequences to be almost four times as high and the age of the most recent common ancestor three times as great as the corresponding values of humans. Phylogenetic analyses show the sequences from the different chimpanzee subspecies to be intermixed and the distance between some chimpanzee sequences to be greater than the distance between them and the bonobo sequences.