Transrectal longitudinal ultrasonotomography of the prostate with the newly developed electronic linear scanning method was done on 100 cases and the characteristic echo patterns for each prostatic disease were obtained. With this method we can observe real-time longitudinal tomograms of the prostate, seminal vesicles and bladder. Real-time observations make it easier to examine the relationship between the prostate and its surrounding organs, especially the bladder neck and the prostatic urethra, at the time of urination.