A series of 4a-methyl-3,4,4a,9-tetrahydrophenanthrene-2-carboxylic acids and 2-phosphinic acids has been prepared and evaluated in vitro as inhibitors of human recombinant steroid 5a-reductase. 7-Chloro-4a-methyl-3,4,4a,9-tetrahydrophenanthrene-2-carboxylic acid, 5, is a marginally selective inhibitor of human type 2 steroid 5a-reductase (Ki - 260 nM). The phosphinic acid compounds, 8 and 9, are weak inhibitors of types 1 and 2 steroid 5a-reductase.