AIM: To study gender difference in nimodipine (NMD) pharmacokinetics in rats after oral administration NMD and co-administration erythromycin (Ery). METHODS: NMD concentrations in plasma were determined by HPLC after ig administration of 20 mg·kg -1 NMD and co-administration of 50 mg·kg -1 Ery,respectively. RESULTS: Marked gender differences for NMD concentrations in rat plasma were found after oral administration of 20 mg·kg -1 NMD. In groups of NMD alone,the plasma concentrations of NMD in male rats were significantly (P< 0.05 ) lower than those in female rats. AUC value of NMD in male rats was only about one-fourth of that in female rats. In groups for co-administration of Ery,there also exists gender difference;the concentrations of NMD in male rats also were significantly (P< 0.05 ) lower than those in female rats and AUC value of NMD in female rats was about 3.4 -folds of that in male rats. In addition,NMD concentration in plasma was significantly increased after co-administration Ery,which AUC values increased 2.0 -and 1.6 -folds of those in alone NMD,respectively. CONCLUSION: There are marked gender differences in NMD pharmacokinetics of oral administration in rats,and Ery can increase plasma concentrations of NMD.