The ascorbate/urate ratio in the seminal plasma was studied in 76 randomly chosen infertile men. The levels of ascorbate and urate were found to vary widely (range: 93-954 mumol l-1 and 127-670 mumol l-1, respectively), while the ascorbate/urate ratio was 1.03 +/- 0.63 (mean +/- SD), indicating almost equimolar concentrations of both compounds in more than 60% of the subjects investigated. No relationship of ascorbate with any biochemical marker of accessory sex gland secretions was observed, whereas an inverse correlation of urate with some prostatic markers, acid phosphatase (-0.37; P < 0.001), zinc (-0.35; P < 0.002) and citric acid (-0.33; P < 0.003), was found. In vitro experiments were conducted on an artificial suspension containing ascorbate and urate at physiological levels and activated polymorphonuclear leukocytes in the normal range (as proposed by WHO) to determine the extent to which the presence of superoxide anion-generating leukocytes contribute to the depletion of ascorbate and urate. The ascorbate level did not change in the presence of 0.2 x 10(6) leukocytes ml-1, while higher amounts of activated polymorphonuclear leukocytes initiated ascorbate oxidation, the intensity of which was in correlation with the extent of leukocyte contamination. After incubation (37 degrees C, 30 min) in the presence of 0.4, 1.0 and 1.5 x 10(6) cells ml-1, the average decline from the initial ascorbic acid level was 24, 43 and 49%, respectively. However, exposure of whole semen, instead of buffer, to oxidants released from the same amount of activated polymorphonuclears led to only 2.6, 11 and 22% decrease of the ascorbic acid, most probably due to the action of other superoxide anion scavenger compounds present in semen. Excessive superoxide anion production due to the presence of activated leukocytes had no influence on urate level either in the artificial suspension or in semen. The ability of ascorbate to afford protection against leukocyte-associated superoxide anions is not hampered in the semen of infertile men, provided that leukocyte contamination does not exceed 1 x 10(6) cells ml-1. The possible role of urate in stabilizing the ascorbate antioxidant activity in seminal plasma should be further investigated.