We identified the collagen type and content of the tunica albuginea in Peyronie's disease and venogenic impotence compared with the tunica albuginea from the donor of the renal transplant and patients with penile injury. Type III collagen was detected obviously in Peyronie's plaque and was also present in venogenic impotence. It can be hardly found in normal controls. The ratios of type III to type I collagen were significantly higher in Peyronie's plaque while there was a moderate increase in venogenic impotence. The scarcity of type V collagen was noted in human tunica albuginea. The decreased percentage of glycine and alanine in Peyronie's disease and venogenic impotence implied the abnormal composition of collagen or presence of noncollagen protein. The results suggest the biochemical aberration of the tunica albuginea might interfere with the normal function of the penile drainage system.