This paper was to investigate the biovailability of antipyrine, ampicillin and protein binding in pathological rats and rabbits pretreated with typhoid vaccine. The results are as follows: The absorption of antipyrine and ampicillin respectively were reduced in rats pretreated with typhoid vaccine as compared with those of normal rats. Especially absorption of ampicillin was more decreased than those of antipyrine. The blood level of antipyrine in severe state was decreased but in mild state. Blood level of ampicillin was decreased in mild state as well as in severe state. Relative bioavailability of antipyrine and ampicillin were mostly decreased in rabbits pretreated with typhoid vaccine except that of antipyrine in mild state. Renal clearance of antipyrine was not affected, but that of ampicillin was apt to increase. Protein binding of antipyrine and ampicillin were decreased by high concentration of typhoid vaccine.