Starch-gel electrophoretic characteristics of the hemoglobins, muscle myogens, serum transferrins, and serum esterases from two species of mouth brooders, T. mossambica Peters and T. hornorum Trewavas, and two species of substratum spawners, T. zillii Gervais and T. melanopleura Dumeril, are described in detail. The mobility characteristics of lactate dehydrogenases (LDH) from 11 tissues of these four species are also described.The two mouth brooders possess virtually identical LDH zymograms, whereas the unique mobility difference of the skeletal muscle type subunit distinguishes T. zillii from T. melanopleura and from the two mouth brooders. The LDH subunit specific for the eye tissue comprised the major diagnostic feature distinguishing the mouth brooders and the substratum spawners.No mobility differences in serum esterases were found between the two substratum spawners, whereas the mouth brooders did possess different mobilities. Tilapia mossambica possessed a single serum transferrin zone, and T. hornorum one major and one minor zone.The hemoglobins and muscle myogens completely separated all four species of Tilapia indicating that these are the protein groups of choice as diagnostic tools in their identification. These proteins are likewise sufficiently diagnostic to point out that the specimens of T. mossambica and particularly T. hornorum used in these studies were not always biochemically uniform, emphasizing their further value in the selection of parental stocks for breeding purposes. The need for new approaches such as these for supplementing the classical morphometric techniques in fish farming is outlined.