In the great lakes of Africa, endemism and high rates of speciation are characteristic for some genera within cichlid species flocks. These flocks present novel problems in differentiation and speciation. Much debate has centered around the actual way in which speciation has taken place in the African lakes and in particular whether or not the cichlid flocks provide an example supporting sympatric as opposed to allopatric speciation. To characterize evolutionary changes in some species of the presumed young species flock of Lake Victoria, we studied allozyme variation through electrophoretic analysis of muscle enzymes from 10 haplochromine species. The genetic similarities calculated between the 8 Haplochromis species are very high (genetic identities are all higher than 0.97). Even the monotypic genera Hoplotilapia retrodens and Macropleurodus bicolor are electrophoretically indistinguishable from members of Haplochromis. Based upon the available evidence, the species used here are biologically valid. Therefore it is argued that the very high genetic similarities reported here (and by other authors) are best explained by a very recent separation of the different haplochromine gene pools. This implies that the genetic differences, which did accompany reproductive isolation, involved either regulatory genes or non enzymatic parts of the structural genome. This is in accordance with the accepted views on the dominant factors in cichlid speciation.