The small GTP-binding protein family regulates various cell functions in mammalian and yeast cells. In the yeast Saccharomyces cerevisiae it has been known to be involved in vegetative growth. As an initial attempt to explore the involvement of CDC42, a member of this family, in the regulation of morphological changes in Candida albicans, we isolated a gene encoding this protein (CDC42Ca) from this fungus. The sequence of isolated gene revealed an open reading frame of 570 nucleotides with the potential to encode a protein of 190 amino acids with a predicted molecular weight of 20.5 kDa. The deduced amino acid sequence was highly homologous to CDC42s from yeast (87.8%), human (76.4%) and Caenorhabditis elegans (73.7%). The CDC42Ca mRNA level showed a transient increase with a peak at 2 h after the fresh medium shift (28 degrees C) when cells synchronously formed buds, whereas it displayed a gradual increase up to 12 h after the medium shift (37 degrees C) with elongation of germ tubes. This suggests that CDC42 may play a role in the bud emergence and also germ tube formation in C. albicans.