Abstract: The present paper describes the pharmacokindtics and pharmacodynamics of CTX in both normal control rats and early alloxan-diabetic rats in vivo. The plasma concentrations of CTX were determined with HPLC. The main pharmacokinetic parameters of the two groups were calculated with computer.Compared with the control group, t冰Cand AUC in the diabetic group decreased significantly. Most of the free drug was distributed to tissue fluid because the protein binding of CTX decreased. But ,the T_1/2 ka and T_1/2 ke of the two groups were not significantly different. It was suggested that the absorption and elimination rate of CTX were not affected in early diabetic rats. The PD₅₀ of CTX against S. Pneumonias infection was not different significantly between the two groups.This implies that the therapeutic effect of CTX was enhanced as the plasma free concentration could be increased in diabetic ratts.