Some aspects of the regulation of carotenoid biosynthesis in immobilized Gibberella fujikuroi mycelia were studied and the results compared to those obtained from freely suspended mycelia. Nitrogen limitation induced carotenoid biosynthesis in immobilized G. fujikuroi mycelia under non-limiting carbon conditions. In addition, certain water soluble polyketide like red pigment was synthetised and released into the culture medium under same conditions. It was found that carbon/nitrogen ratio plays an important role in carotenoid biosynthesis and it determines the extension of its production. Noticeable differences were also found in type and quantity of other secondary metabolites produced by both immobilized and freely suspended mycelia of G. fujikuroi. Photoinduction of carotenoid biosynthesis in immobilized mycelia was also studied. The results suggest that regulation of carotenoid biosynthesis is qualitatively similar to that observed in freely suspended mycelia and is shown to be enhanced by immobilization in natural polymers. (C) 2003 Elsevier Inc. All rights reserved.