Racemic limonene was enantio-selectively and enantio-specifically converted to (R)-(+)-alpha-terpineol by Penicillium digitatum mycelia. Bioconversion only occurred during the early to mid-log phase of growth. This pattern held true when different age inocula were used. Bioconversion activity increased more than 4-fold after substrate induction. Aeration was critical to this bioconversion. The optimum oxygen requirement was 1.6 mg/litre. Up to 4% (v/v) limonene did not inhibit the bioconversion. cr-Terpineol inhibition was seen at concentrations greater than 25.9 mM. The optimum conversion temperature was 28 degrees C, and the optimum pH was 4.5. The highest concentration of product was formed with a contact time of between 1 and 2 days.