The present work studied the effect of the organophosphate insecticide, sumithion on the liver of toads Bufo tibamicus. Feeding toads with a daily dose of sumithion ( 40 mg / kg body weight ) for 10 days caused histological alterations in the liver . The normal structural organization of the hepatic acini was impaired , the hepatocytes showed cytoplasmic vacuolation and the blood vessels were congested . Moreover, elevations of transaminases ( GOT , GPT ) were recorded in the sera of treated animals . The obtained results collectively indicated that sumithion treatment induced liver injury in the toads .