For direct identification of Candida albicans from other Candida species, the chlamydospore formation and the mycelial transition induced by high temperature and by sera were examined in 198 Candida isolates. The germ tubes of C. albicans developed early at 30 min in high temperature-induction, but at 60 min in serum-induction. C. albicans generated germ tubes well at concentrations lower than 2 x 10⁷ cells/ml, but the germ tube formation was markedly restrained at concentrations higher than 4 x 10⁷) cells/ml. In a serum-free, yeast extract-peptone-dextrose (YEPD) medium, C. albicans grew as a yeast form at 30 ℃ and as a mycelial form at 35-42 ℃. Mycelial development was maximal at 37 ℃ in serum and at 39 ℃ in YEPD. Germ tubes were formed within 30 min in YEPD at 39 ℃, but after 60 min in serum at 37 ℃. Our examination showed that the 39 ℃-induced germ tube formation tests were very reliable (sensitivity 100%, specificity 100%) at discerning C. albicans from other Candida species. These results suggest that the high temperature-induced germ tube formation testing could be a useful identification method of C. albicans in clinical laboratories.