In past studies erformed to differentiate among commercially important species of the Tilapia group, erythrocytes o the different species were successfully investigated in agglutination tests with lectins and Tilapia antisera. The present publication reports on WESTERN blot analyses of humoral plasma proteins from Oreocbromis aureus (Steindachner 1864), O. niloticus (Linne 1766) and Sarotherodon galilaeus (Artedi 1757). For lectin blots, in addition to comlete plasma samples, N-acetyl glucosamine tearing plasma glycoproteins were investigated after their affinity-chromatographical isolation from the plasma using a WGA agarose column. For immunoblots, only complete plasma samples were used. After SDS treatment the samples were electrophoretically separated and transferred onto nitrocellulose membranes. The transferred proteins were then tested for their reactions with lectins and antisera. In all cases the employed indicator molecules showed species-specific differences, enabling a clear identification of the investigated species.