A review, with 47 refs. and with particular emphasis on biotransformation of ricinoleic acid or its esters to gamma-decalactone in presence of various yeast strains. Yarrowia lipolytica yeasts were used for cyclization of castor oil-contained 4-hydroxydecanoic acid (oil content 10%) to gamma-decalactone at 28 degrees C for 8-9 days. The product was recovered from the reaction mixt. by steam distn. (yield 91% at pH 2).