The pharmacokinetics of cefdinir were investigated in six hemodialysis patients. For the present study, two tests were carried out, one with 4 h of hemodialysis and the other without hemodialysis. Cefdinir was given orally to each patient in a dose of 100 mg, and blood was collected serially for 48 h after dosing in the test without dialysis and for 72 h in the test with dialysis. In the test without dialysis, the maximum plasma concentration (C_max) was 2.36 ± 0.53 µg/ml (mean ± standard deviation) and the time to C_max was 9.00 ± 2.45 h. The terminal elimination half-life (t_1/2) and area under the concentration-time curve (AUC) were 16.95 ± 1.20 h and 69.05 ± 14.84 µg · h/ml, respectively. In the test with dialysis, t_1/2 during hemodialysis decreased approximately to one-sixth of that obtained in the test without dialysis, although t_1/2 in the latter elimination phase did not differ from that in the nondialysis test. AUC was reduced to 43% of that in the test without dialysis. The fractional removal of cefdinir by hemodialysis was 61%. These findings indicate that clearance of cefdinir is prolonged in patients with renal failure, and cefdinir is well removed by introduction of hemodialysis, although t_1/2 (during hemodialysis) and AUC were two and eight times higher than the data previously reported for healthy volunteers, respectively. The pharmacokinetic data suggest that 100 mg of oral cefdinir once a day would result in a sufficient concentration in plasma in hemodialysis patients, but this remains to be confirmed by multiple-dose studies.