It was to investigate the absorption, excretion, protein binding of ampicillin in the pathological animals pretreated with carbon tetrachloride and mercuric chloride. The absorption of ampicillin was not affected in rats with damaged liver and kidney as compared with that of normal rats. The blood level of ampicillin after oral administration was increased significantly in rabbits with damaged kidney and liver. The blood level of ampicillin in rabbit with damaged kidney was more increased than that in rabbits with damaged liver. In severly damaged rabbits, it was more increased than that of mildly damaged rabbits. Urinary excretion of ampicillin in pathological animals was more inhibited than that of ampicillin in normals. Hepatic excretion of ampicillin was accelerated in rabbits with damaged kidney. However, in rabbits with damaged liver, it was inhibited as compared with that in normals. Protein binding of ampicillin was slightly enhanced by the various concentration of carbon tetrachloride and mercuric chloride, respectively. The results suggest that the increase of blood level of ampicillin in pathological animals was due to the inhibition of renal excretion.