In a series of approximately 400 patients investigated for oligospermia 4 had small testicular tumors demonstrated by high resolution real-time ultrasound. The lesions ranged in size from 3 to 6 mm., were clinically impalpable and were demonstrated on repeated sonograms. Exploration was done in all 4 patients with the aid of intraoperative high resolution ultrasound. This procedure allowed for conservative resection of the tumor with preservation of the testicle. The pathological diagnosis in all cases was benign Leydig cell tumor.