A Mucor sp. isolated from soil and identified as Mucor piriformis was used to study the mode of transformation of progesterone. Major metabolites isolated and identified were 14α-hydroxyprogesterone, 7β, 14α-dihydroxyprogesterone, 7α, 14α-dihydroxyprogesterone, and 6β, 14α-dihydroxyprogesterone. Among the minor metabolities, 5β, 14α-dihydroxy-pregnane-3, 20-dione has been characterized. Time-course studies of the formation of transformation products showed that hydroxylation at the 14α-position is the first step in the formation of dihydroxyprogesterones. The formation of 7β, 14α-dihydroxyprogesterone and 5β, 14α-dihydroxypregnane-3, 20-dione represents novel transformations by Mucor species.