The chromosome aberration assay (CA) in bone marrow cells and the micronucleus test (MNT) in both bone marrow and peripheral blood erythrocytes have been carried out for the evaluation of the clastogenic potential of acephate (asataf) in a chick in vivo test system. Technical grade acephate was administered to evaluate dose-responses (25, 50 and 100 mg/kg), route-responses (i.p. and p.o.) and time-responses (6, 24 and 48 h). A comparison of CA frequencies after acute and chronic dosing was also performed. Only 50 mg/kg of acephate induced significant bone marrow chromosome aberrations after 24 h exposure while all three doses induced significant increases in micronuclei in both bone marrow and peripheral blood erythrocytes in i.p. route only. The presented data confirm our earlier reports that the neonatal chicken test system is a convenient model and can be used as an alternative to mammalian systems for screening some environmental contaminants for genotoxicity.