Sporidiobolus salmonicolor, CCRC 21975 was immobilized in kappa-carrageenan, chitosan, agarose or calcium alginate. Due to the detrimental effects of high temperature attained during the gelling processes of kappa-carrageenan and agarose as well as the toxicity of chitosan to the test organism, immobilization of S. salmonicolor with these matrices for the production of gamma-decalactone was inadequate. Neither viable cells nor production of gamma-decalactone could be detected in media after 4 days cultivation of S. salmonicolor immobilized with kappa-carrageenan or chitosan. Fewer viable cells and little gamma-decalactone production was found in media with agarose-immobilized cells. In contrast, no significant reduction in the viable population was noted during immobilization procedures using alginate. Alginate-immobilized S. salmonicolor cells showed less susceptibility to ricinoleic acid toxicity and produced more gamma-decalactone than did free cells. Time courses of gamma-decalactone production by S. salmonicolor also revealed that immobilized cells produced a maximum gamma-decalactone yield of ca. 131.8 mg l(-1) after 5 days fermentation, compared with a maximum of ca. 107.5 mg l(-1) for free cells.