Compounds of structural Formula (I) ##STR1## and pharmacologically acceptable salts and esters thereof possess 5.alpha.-reductase inhibitory activity. These compounds inhibit 5.alpha.-reductase type 1 and type 2. The compounds of structural Formula I are useful in the systemic, including oral, and parenteral, including topical, treatment and prevention of hyperandrogenic conditions including prostatic carcinoma, benign prostatic hyperplasia, acne vulgaris, seborrhea, androgenic alopecia (also called androgenetic alopecia) which includes male- and female-pattern baldness, female hirsutism, and prostatitis. A class of compounds of the present invention are also potent antiandrogens. The present invention also relates to novel compositions containing such compounds, methods of their use and methods of their manufacture.