In order to clarify the value of transrectal ultrasonic examination of the prostate in the diagnosis of prostatic cancer at an early stage, 666 patients were screened in one year; 602 of them (TO) had a normal, firm or hypertrophic but non-nodular prostate at digital rectal palpation, 41 had a T1-T2 prostate and 23 a T3-T4 prostate. Among the 602 TO prostates, 162 showed a hypoechoic peripheral area which was biopsied, revealing an infiltrating carcinoma in 11 cases. The ability of transrectal ultrasound alone to detect TO cancer was estimated at 1.8 per cent (11/602). The positive predictive value of a hypoechoic image of the prostate was estimated at 7 per cent (11/162), which is much lower than the figures reported in the literature. Transrectal ultrasound can be considered an acceptable method for detecting TO tumours of the prostate with a yield comparable to that of digital rectal palpation in the T1-T2 tumours. The low performance (1.8 per cent) of transrectal ultrasound in detecting cancer at an early stage rules out any mass screening programme of the male population over 50 years of age. However, 45 per cent of localized tumours in this series were detected by transrectal ultrasound.