The relationship between prostate specific antigen (PSA) levels, prostate volume and age was examined in 472 men who underwent PSA assay (Hybritech), digital rectal examination (DRE) and transrectal ultrasound (TRUS) as part of a community survey of benign prostatic hyperplasia following exclusion of men with prostate cancer. The mean age of the study population was 60 years (range 40-79). The mean PSA was 2.4 ng/ml and 85% of the men had levels < 4 ng/ml. There was a modest correlation between PSA and both age and prostate volume. The mean prostate and adenoma volumes were 32 ml (SD 13.4) and 15 ml (SD 10.7) respectively. Prostate volume increased with age. Linear regression analysis revealed an independent association between PSA and age when controlling for volume. The mean ratio of PSA per unit of prostate volume was 0.072 ng/ml. This ratio also increased with age. Age and prostate volume influences PSA levels independently. The sensitivity and specificity of PSA adjusted for volume and age in the diagnosis of prostate cancer need to be evaluated in association with DRE and TRUS.