The biological characteristics of prostate-specific antigen were studied in the Nigerian African. Two hundred and fourteen persons were selected for the study. The group was made up of 59 apparently healthy men (age range 22-76 years), 58 men (age range 40-91 years) who had biopsy proven diagnosis of cancer of the prostate gland, 81 men (age range 46-87 years) who had biopsy proven benign prostatic hypertrophy (BPH) and 16 women (age range 23-47 years). Their median ages were 53 years, 66 years, 66 years and 27 years, respectively. The median PSA value among the control population was 0.7 ug/L (range 0.1-4.3 ug/L) and 98.3% of them had PSA of less than 4 ug/L. No person below 50 years of age had PSA value greater than 2 ug/L. There was a significant correlation between age and serum PSA value over the entire age range (r = 0.523; P = 0.001). In the female study group, 4(25%) had detectable values the cause of which could not be determined. The median PSA value among the BPH patients was 8.5 ug/L (range 0.2-350 ug/L). In this group 37% of them had values below 4 ug/L and 54.3% of them had values less than 10 ug/L. Among the patients who had cancer of the prostate gland the median PSA value was 92.6 ug/L and the mode was greater than 350 ug/L (32% of the patients); 10% and 20% of them had values below 4 ug/L and 10 ug/L respectively. It is concluded that the trend is the same as in the studies and there is the need for prostate gland volume studies and evaluation of women who have detectable PSA values.