In an attempt to define whether intravenously administered pefloxacin might be appropriate for surgical prophylaxis in prostatectomy, 50 patients undergoing transvesical prostatectomy for benign prostate hyperplasia were given a single intravenous dose of 800 mg; surgery was then performed after 2, 4, 6, 8 or 10 h. Concentrations of pefloxacin were determined in serum and in both the centre and periphery of the prostate adenoma using a microbiological plate assay. Elevated concentrations of pefloxacin were found in the adenoma from 2 h onwards. The central and peripheral concentrations were similar and had a mean value of 4.39 microg/g of tissue. These concentrations were similar to those achieved in serum. Although concentrations of pefloxacin were not determined separately in the intercellular, interstitial or excreted fluid, the tissue levels found were well above the MICs of pefloxacin for the bacteria commonly causing acute and chronic prostatitis. These data suggest the intravenous administration of pefloxacin to be a satisfactory alternative for the surgical prophylaxis before prostatectomy as well as in the therapy of acute prostatitis.