We studied 155 human short tandem repeat (STR) DNA markers in chimpanzees (Pan troglodytes) via the polymerase chain reaction (PCR). There is no difference in number of alleles per locus among STRs of different motif length (di-, tri-, or tetranucleotide repeats). We investigated 42 of the most informative STRs in greater detail using DNA isolated from a panel of 41 African-born, captive-housed chimpanzees. They reveal a wealth of genetic variability in chimpanzees, with an average of six alleles and 70.6% heterozygosity. The average paternity exclusion probability is 51.6%, and the best three STRs jointly provide >95% mean exclusion probability. Used in combination to define a multiple-locus genotype, the five most informative focal STRs can potentially uniquely identify every chimpanzee alive in the world. Although the subjects are of unknown geographical origin, homozygosity tests indicate little evidence for population subdivision. These markers represent the basis of a powerful battery of genetic tests, including individual identification, e.g., in poaching, paternity testing, or reconstruction of pedigrees among captive and wild chimpanzee breeding populations.