Candida albicans possesses the ability to switch reversibly and at high frequency between a number of heritable phenotypes distinguishable by colony morphology and in some cases cellular phenotype. In the original switching system identified in C. albicans, it was demonstrated that cells could switch at frequencies as high as 10(-2) among seven distinct colony phenotypes including smooth, star, ring, stipple, irregular wrinkle, hat, and fuzzy. In a second switching system first discovered in a systemic infection, cells switched at high frequency between a white and an opaque colony former. Recently, switching was discovered in isolates from patients with vaginal candidiasis and multiple switch phenotypes were cloned from an individual vagina. Switching may contribute to the pathogenesis of C. albicans by providing it with the capacity to invade diverse sites in the body, to change resistance to antifungal agents, or to change antigenicity. The molecular basis of switching is probably due to the reversible transposition or rearrangement of genomic elements, although a direct correlation between recently identified genomic rearrangements and phenotypic switching has not been made.