For perioperative prophylaxis 200 mg ciprofloxacin were administered as a short intravenous infusion to 17 patients aged 57-84 years before transurethral resection (TUR-P) or transvesicular enucleation (TVP) of the prostate. 13 patients were injected simultaneously with 2.5 g ioxitalamic acid i.v. to determine the kidney function. In 11 patients the plasma concentrations were assayed and the pharmacokinetic parameters calculated. At the end of infusion the concentrations of ciprofloxacin in plasma reached 4.2 +/- 0.8 microgram/ml and decreased after a fast distribution period (plasma half-life 0.20 +/- 0.09 h) with a terminal half-life of 4.2 +/- 1.3 h to 0.2 +/- 0.09 microgram/ml after 10 h. The apparent volume of distribution in steady state was 183 +/- 45% of body weight, the plasma clearance 457 +/- 146 ml/min/70 kg. The average concentrations in prostatic adenoma tissue were at all sampling times higher (2fold) than in plasma. The mean concentrations in prostatic secretion were about half of the respective plasma concentrations. High concentrations of the concomitantly administered ioxitalamic acid in prostatic secretion are considered as an indicator of urinary contamination. In those patients high ciprofloxacin concentrations in prostatic secretion are not reliable.