Candida dubliniensis is a recently described pathogenic species which shares many phenotypic features with Candida albicans, including the ability to form germ tubes and chlamydospores. These similarities have caused significant problems in the identification of C. dubliniensis by the average clinical mycology laboratory. To facilitate the differentiation of these species, we investigated the growth of 120 isolates of C. dubliniensis and 98 C. albicans isolates at 42 and 45 degrees C on Emmons' modified Sabouraud glucose agar (SGA) and 10 isolates of each species in yeast-peptone-dextrose broth. None of the C. dubliniensis isolates grew on the agar or in the broth medium at 45 degrees C, while 11 isolates were capable of growing on SGA at 42 degrees C. In contrast, all of the C. albicans isolates but one grew at 45 degrees C on or in either medium. These reproducible results clearly demonstrate that the incubation of isolates suspected to be C. dubliniensis or C. albicans at 45 degrees C provides a simple, reliable, and inexpensive method for the differentiation of the two species.