Esters and hydrocarbons, containing 14 and 15 carbon atoms, are converted to the hydroxy fatty acid portions of glycosides byTorulopsisapicolain yields of 10–20%. When C-15 compounds are fermented, almost half of the hydroxy acids which are produced are 16-hydroxy C-17 acids. The carbon chain of the substrate is first lengthened by two carbon atoms and then hydroxylated. Direct hydroxylation also occurs, to a lesser extent, giving both 14-hydroxy- and 15-hydroxypentadecanoic acids. Similar results are obtained when C-14 compounds are used. Lengthening of the chain followed by hydroxylation gives rise to hydroxy C-16 acids and direct hydroxylation produces 13-hydroxy- and 14-hydroxytetradecanoic acids. Primary and secondary C-14 and C-15 alcohols were also isolated from the products of hydrocarbon fermentation (2.5–5 % yield). Methyl palmitoleate is converted to hydroxy fatty acids in yields of 40–70%, the major component of which is 16-hydroxy-cis-9-hexadecenoic acid.