A versatile fungus isolated in our laboratory and identified asMucor piriformis has been shown to effect novel and preparatively useful transformations in steroids and morphine alkaloids. The organism very effectively carries out hydroxylation of various C19 and C21 steroids at 7 and 14-positions. Although the organism is capable of catalysing hydroxylation at 6β and 1lα-positions, these are not the major activities. The 14α-hydroxylase appears to have a broad substrate specificity. However, steroids with a bulky substitution at C-17 α-position or without the 4-en-3-one group are not accepted as substrates by the 14α-hydroxylase system. Studies have demonstrated how various C19 and C21 steroids can be modified to yield new structures which are either difficult to prepare by traditional methods or hitherto unknown. The organism also very efficiently and selectively carries out the N-dealkylation of thebaine and its N-variants. Interestingly, the nor-compound formed does not get further metabolized. Since thebaine is very often used as a starting material to synthesize various morphine agonists as well as antagonists, and one of the steps involved in their preparation is the N-dealkylation reaction, the microbial process could certainly offer an alternative approach.