Endorectal ultrasound of the prostate with color Doppler is a new technique to identify internal vasculature and flow. In a period of one year more than 500 men have been examined with this technique. The normal prostate will demonstrate flow within the surrounding vasculature; there is no distinguishing flow among the various zones. In prostate cancer there is an increased flow within or surrounding the lesion. Diffuse prostatitis exhibits a diffusely abnormal flow; in focal prostatitis the flow is not significantly different from cancer. In benign prostatic hyperplasia a significant abnormal flow was seen, usually in the inner gland, and flow was frequently identified in the area of the surgical capsule. Color Doppler can provide additional physiologic information for prostate ultrasound and may increase the specificity and sensitivity of the examination in the evaluation of potential prostatic malignancy.