Candida albicans formed germ tubes within 3 h at 37C in a glucose–salts–biotin (GSB) medium containing L-alpha-amino-n-butyric acid as the nitrogen source. Optimal germ-tube production was obtained when the inoculum was grown on Sabouraud dextrose agar. The GSB medium containing L-alpha-amino-n-butyric acid promoted germ-tube formation more effectively than GSB medium plus gamma-amino-butyric acid or Sabouraud dextrose broth.Carbon-14 incorporation studies revealed that during germ-tube formation (0–4 h) the 3 carbon of alpha-amino-n-butyric acid was incorporated intracellularly to a greater extent than the 1 carbon. However, during blastospore formation (5–16 h), this difference was less pronounced.When six other Candida species were grown in GSB plus L-alpha-amino-n-butyric acid medium, few germ tubes were observed with the exception of one Candida stellatoidea strain. However, even this strain of C. stellatoidea produced far fewer germ tubes in this minimal culture medium than any strain of C. albicans tested.