Production of chlamydospores on casein agar at 24°C for 48 h provides a simple means for differentiating Candida dubliniensis from Candida albicans based on chlamydospore production. Of 109 C. dubliniensis isolates tested on this medium, 106 (97.2%) produced abundant chlamydospores and three produced few chlamydospores. In contrast, of the 120 C. albicans isolates tested, 111 (92.5%) failed to produce any chlamydospores, whereas the remaining nine isolates produced few chlamydospores. These findings indicate that abundant chlamydospore production on casein agar is a useful test for discriminating between C. dubliniensis and C. albicans.Since its first description in 1995, Candida dubliniensis has been isolated from a variety of specimens from humans in countries all over the world (6,13,15,(18)(19)(20). As a consequence of the increasing number of reports on the isolation of C. dubliniensis, it is important to be able to rapidly and accurately identify this species in most clinical mycology laboratories. However, identification of C. dubliniensis is hampered by its close relationship with Candida albicans, a situation that has sometimes led to the misidentification of isolates of C. dubliniensis as C. albicans (19). At present, the most accurate differentiation between isolates of the two species is performed in reference laboratories with the use of molecule-based techniques such as PCR or DNA fingerprinting with repetitive sequence-containing DNA probes (5,17,19). However, these sophisticated techniques are not suitable and often not readily applicable for use in small clinical mycology laboratories, where simple and rapid methods are needed. Reliable phenotypic methods for the identification of C. dubliniensis isolates include carbohydrate assimilation profile analysis by using commercially available yeast identification systems and detection of differential antigen expression by immunofluorescence microscopy (2,3,11,12,20). Furthermore, a variety of other ancillary tests have been developed for discriminating between C. dubliniensis and C. albicans isolates, including the inability of C. dubliniensis to grow at 45°C (12). However, whereas these tests are useful for the presumptive identification of C. dubliniensis, they are not definitive. One of the key features employed in the initial description of C. dubliniensis was its ability to produce abundant chlamydospores on cornmeal agar and rice-agar-Tween-agar (20). Chlamydospore production by C. dubliniensis on Staib agar and caffeic acid-ferric citrate agar has also been used recently for the differentiation of C. dubliniensis from C. albicans (1,17). In the present study, the production of chlamydospores by C. dubliniensis and C. albicans on casein agar was investigated as an additional means for differentiating the two species.The reference and clinical isolates used in this study are shown in Table 1. Conventional morphological and physiologic methods, as well as molecular techniques, were employed to confirm the identity of all isolates (1,2,4,5,11,19). ...