To reevaluate the clinical usefulness of erection penography for diffential diagnosis of impotence, we reviewed retrospectively the data of penography in 56 patients who were diagnosed as impotence by various diagnostic workup. Twelve normal males were studied as control group. Papaverine HC1 30mg was injected into the corpus cavernosum and simultaneously Tc HAS 20mCi was injected via an antecubital vein. After injection radioactivities in the penile area were detected for 30 minutes by gamma camera and time activity curve was displayed, We defined that transit time(TT) is the time to reach peak activity and erection persistent time(EPT) is the duration of time to maintain peak activity and venous index( VI ) is the ratio of radioact,ivity(R3Q/R ,). The result.s were as follows : The TT of arteriogenic group(10.7+2.8min) was significantly increased compared with those of control and venogenic groups(P<0.05, respectively). The EPT of venogenic group (6.2+6.8min) is significantly decreased compared with those of control and arteriogenic groups(P<0.05, respectively). The TT of psychogenic(15.2+5.5min) is significantly increased compared with those of control and arteriogenic groups(P<0.05, respectively). In conclusion erection penography was very useful for the diagnosis of vascular and psychogenic impotence and for differentiation between arteriogenic and venogenic but it could not differentiate mixed type or neurogenic from vascular or psychogenic.