SummaryThe pattern obtained by evidencing the activity of certain enzymes following electrophoresis of red cell hemolysates, varies from one individual to another.With regard to the enzymes under consideration (acid phosphatase, phosphoglucomutase, adenylate kinase, adenosine deaminase, glutamic-pyruvic transaminase, phosphogluconate deshydrogenase, etc...), this polymorphism is determined by a simple genetic system, does not correspond to any pathology, and belongs therefore to the concept of“blood group”.Besides their theoretical interest, these group systems are very useful for resolving some problems of applied human geneties, particularly for the diagnosis of mono- or dizygotic twins and for medico-legal cases of disputed paternity.