The objectives of this proposal are the synthesis of specific 5,10-seco steroids and their evaluation as selective inhibitors of steriod-transforming enzymes. Some of these steroid analogs are designed as active site-directed irreversible inhibitors of Delta 5 minus 3-ketosteroid isomerase of 3- and (3 and 17) Beta-hydroxytsteroid dehydrogenases and of processes involved in the oxidative degradation of lanosterol and of cholesterol. Others are intended to be reversible inhibitors of these enzymes. The mechanisms by which enzyme inhibition occurs, will be studied.