The corporeal blood gas changes in accordance with the duration of the prolonged erection which developed after intracorporeal pharmacotherapy with papaverine and phentolamine were investigated in 62 impotence patients. The picture of the corporeal blood taken from 15 psychogenic impotence patients (a control group) at 10 minutes after intracavernous injection when they showed full erections was arterial but there was pCO2 rise and pH drop compared to femoral artery blood taken simultaneously. As the erection lasted longer, significant gas changes of the cavernous blood began to appear (p<0.0001): increase in pCO2 and decrease in pO2 from 4 hours, decrease in pH from 5 hours, decrease in O2 saturation from 6 hours. Erections lasting for more than 16 hours showed significantly worse hypoxia (p<0.05). Therefore, to prevent hypoxia and metabolic acidosis, drug-induced prolonged erection would be better decompressed before it lasts for more than 4 hours.