During the past year a total of 296 transrectal ultrasonic prostatic scans were performed on 267 patients. Four groups of patients were evaluated: (A) previously untreated patients presenting the symptoms of bladder outlet obstruction; (B) patients referred for evaluation of prostatic nodules; (C) patients with newly diagnosed prostatic malignancies being considered for radical prostatectomy; and (D) patients previously diagnosed with prostatic malignancies having been treated either with radical prostatectomy, radiation therapy, hormonal therapy, or chemotherapy. Studies to date indicate that though some patients with clinically unsuspected carcinoma can be diagnosed by ultrasonic studies false negative studies do occur as evidenced by three patients with clinically benign disease, negative scans, and evidence of carcinoma in tissue removed at time of simple prostatectomy. Due to the time consuming nature of the procedure and the relative expense it would appear that prostatic ultrasonography would not be of great benefit as a screening procedure in a clinically asymptomatic population. In selected patients however prostatic ultrasonography is of value. It is most helpful in the staging of patients with known carcinomas and in the evaluation of patients with prostatic nodules. In addition ultrasonography is useful in detecting tumor reactivation before it is evident on rectal examination. Studies are also in progress to evaluate the ability of the procedure to measure tumor response to chemotherapeutic agents.