The objective was to devise local guidelines for the referral of patients with suspected prostatic carcinoma following evaluation by a retrospective audit of the value of the prostate-specific antigen concentration, together with age, urological symptoms, and digital rectal examination in the diagnosis of carcinoma of the prostate. Relevant details were collected from the notes of 582 patients from general practice and hospital. The significant diagnostic factors were ascertained by stepwise logistic regression. Prostate-specific antigen concentration, digital rectal examination and significant terminal dribbling were the most powerful factors in the diagnosis of carcinoma of the prostate. When prostate-specific antigen concentration was considered in isolation, a value of 6.5 ng/ml appeared appropriate for referral. Age was not significant, perhaps due to the narrow patient age range. The significant diagnostic factors were built into an algorithm calculating the probability of carcinoma of the prostate. This algorithm, together with prostate-specific antigen concentration results and digital rectal examination findings, forms the basis of the referral guidelines and a subsequent prospective study.