The spermatozoa. of eight species from three groups of the anuran genus Physalaemus were compared cytochemically using toluidine blue (TB) and alkaline fast green (AFG) staining. Different responses were obtained with TB staining, viz Physalaemus centralis and Fl petersi spermatozoa stained greenish, P. lisei spermatozoa stained bluish, P. riograndensis spermatozoa stained blue and P. biligonigerus, P. fuscomaculatus, Fl cuvieri and P. gracilis spermatozoa stained violet. Most of the species showed positive AFG staining, but P gracilis spermatozoa were AFG negative, even after deamination. These results indicate the presence of different rates of Arg/Lys exchange in the cells of these species of Physalaemus. This is the first report of intrageneric variation in composition of sperm basic protein in Leptodactylidae.100395147157