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DIMORPHISM in fungi is generally defined as a reversible transition from a yeast habit of growth (Y) to a mycelial one (M)1. In Candida albicans Y→M transition can occur rapidly in serum2,3, serum substitutes and other natural4–6and synthetic media7. In a few hours the yeast cell or blastospore forms a germ tube which grows as a true mycelium6,8,9. Since the cellular form depends on wall construction10, marked modifications in the organisation of wall components are expected to, and in fact do, occur during morphogenesis. Nevertheless, there is chemical11, cytochemical and ultrastructural evidence12,13that the differences between Y and M walls of C. albicans are essentially quantitative, strongly suggesting that hyphal conversion in this yeast is controlled by the modulation of pre-existing enzymatic activities rather than by any new factors.