The steady-state concentrations of metronidazole and tinidazole in male genital tissues were analyzed in patients subjected to elective gonadal surgery. The nitroimidazoles were administered orally at 500 mg every 8 h, beginning 5 days before the operation. Eight hours after the last dose, the concentrations of tinidazole were 24.1 +/- 2.5 micrograms (mean +/- standard error of the mean)/g of prostatic tissue, 29.1 +/- 2.9 micrograms/g of vas deferens, 22.1 +/- 2.1 micrograms/g of epididymis, and 18.6 +/- 2.3 micrograms/g of testis. The corresponding values of metronidazole were 14.3 +/- 1.8 micrograms/g, 15.9 +/- 1.2 micrograms/g, 14.0 +/- 1.2 micrograms/g, and 12.5 +/- 1.7 micrograms/g, respectively.