Seminal plasma zinc (SP Zn) determinations were undertaken in 22 patients suspected of having chronic bacterial prostatitis and in 12 normal subjects free from prostatic infection. Of the 20 patients with positive Staphylococcus culture 17 (85%) showed the same bacterial growth in urethral urine with no significant difference in colony counts (P > 0.005). Mean SP Zn concentration in seminal plasma of 20 patients (164.69 +/- 122.25 mg/ml) was not significantly different in comparison with the control group (168.47 +/- 123.01 mg/ml) (P = 0.755). Mean SP Zn concentration of 3 (15%) patients (156.95 +/- 98.44 mg/ml), with staphylococcal infection bacteriologically localized to the prostate was not significantly different from those of the control group (P = 0.77). We believe that assays of SP Zn content might aid in the confirmation of the role of Staphylococcus in the aetiology of chronic prostatis in larger patient groups.