The study comprised 24 male and 24 female patients treated either for uncomplicated gonorrhoea or as a prophylaxis. A single dose of 800 mg of bacampicillin + 1.0 g probenecid was administered orally to each patient. The concentrations of ampicillin in urethra and cervix were assayed by means of alginate swabs that were used as diffusion centres on agar diffusion plates. The inhibition zones were compared with a standard series of swabs containing known amounts of ampicillin. The amounts of secretions absorbed into the swabs were determined by weighing each swab before and after taking the specimen. The median ampicillin concentration in the male urethra one hour after the single dose of bacampicillin plus probenecid was 2.0 micrograms/ml of urethral secretion and increased to 3.2 micrograms/ml two hours after administration of the antibiotic. In the female urethra, the median concentrations of ampicillin were 1.5 micrograms/ml and 2.3 micrograms/ml of urethral secretion one and two hours, respectively, after the same dosage as above. The corresponding ampicillin concentrations in the cervical secretion were 1.6 micrograms/ml and 2.9 micrograms/ml, respectively.