Developments in medical intervention and the increasing population of patients with immunodeficiencies and transient or long-term immunosuppression have increased the list of yeast species that can cause disease. Candida dubliniensis is a novel species with close genetic relatedness to C. albicans. The two species share many common physiological and biochemical properties thus making their distinction cumbrous. A rapid and inexpensive way to presumptively differentiate between the two species, having previously performed a germ tube test, is the ability of C. dubliniensis to reduce the tetrazolium salt and it is reported for the first time. Microbiological information about new and emerging yeast pathogens, including rapid means for their identification, equips medical microbiologists with the means to identify and physicians to treat effectively infections attributed to unusual yeasts.