A series of mutants which are blocked at various stages of the sterol degradative pathway have been isolated from the potent sterol degrader Mycobacterium fortuitum ATCC-6842. Sitosterol bioconversions by these mutants result in the accumulation of a number of intermediate compounds, some of which are potentially useful as substrates in the manufacture of medically important steroids. These intermediates include androst-4-ene-3,17-dione, androsta-1,4-diene,3,17-dione, ring A-degraded tricyclic compounds and various 9alpha-hydroxy-steroids.