Random Amplified Polymorphic DNA (RAPD) analysis was applied to three species of the tilapia genus Oreochromis and four subspecies of O. niloticus. Thirteen random 10-mer primers were used to assay polymorphisms within and between populations. Different RAPD fragment patterns were observed for different species, although not always for different subspecies. Evidence is presented that RAPD markers might be useful for systemic investigation at the level of species and subspecies.