The present invention relates to novel substituted 15-oxa-, 15-thia-, and 15-aza- dihydrolanosterols, to pharmaceutical compositions containing such compounds, and to methods of using these compounds to suppress the activity of 3-hydroxy-3- methylglutaryl coenzyme A reductase (HMGR), an enzyme which is important in cholesterol biosynthesis. The overall effect of these heterocyclic lanosterol analogs is to decrease cholesterol formation, thereby resulting in lower serum cholesterol levels in mammals, and impaired ergosterol synthesis in fungi.
