A small computer (HITAC-10 8 K words) was interfaced to a 4 channel renogram unit and time activity curve was analyzed to get functional. From a radiocardiogram, cardiac output was determined. The value obtained by a computer method was comparable to that by manual calculation. From a renogram, effective renal plasum flow was determined. In such a procedure, it was important to measure radioactivity of administered dosage and obtained plasma precisely. We have also applied this method to analyze radioisotope penogram. Radioisotope penogram was used to differentiate functional and organic impotence. The blood volume of erected penis was calculated with ^<99m>Tc labelled autologus red blood cell. When the blood volume reached 30ml erection was obserbed.