Penile erection is related to the integrity of penile tissue. In order to study the ultrastructural histopathological changes in penile erectile tissue in impotent men, biopsies were taken from 29 impotent and 5 normal patients during surgical treatment. Light microscopy revealed insignificant histological changes and various degrees of fibrotic change in the corpora cavernosa of impotent men, and electron microscopy revealed severe myopathic, fibrotic changes in the penile tissue. These non-specific changes could not be used to determine the aetiology of impotence, and the relationship between the ultrastructural appearances, the causes of impotence and the results of treatment was unclear. Further studies are required to establish the value of intracorporeal biopsy in selecting treatment for impotent patients.