Sixty men (7 normal, 53 with prostatic disease) underwent transrectal ultrasonic scanning of their prostates in order to assess the technique and evaluate its reliability in the detection and staging of prostatic cancer. The prostatic capsule was clearly seen in 58 men; non-integrity of the capsule occurred only in those with proven cancer (17 cases). An ultrasound diagnosis of cancer was made for 32 of 33 men with proven disease and it was shown that ultrasound demonstrated anterior perforations of the capsule in 6 out of 18 men with tumours that had been judged by rectal palpation to have been confined to the prostate. It is concluded that transrectal ultrasound is a promising technique of imaging the prostate, particularly in relation to selection of patients for biopsy and for checking staging of cancer carried out by digital assessment of the prostate.