The ultrastructures of colonies of two stable UV-induced morphological mutants and their parental strain of Candida albicans grown on glucose-containing solid medium were investigated by scanning electron microscopy. The structures and ultrastructures of these three types of colonies were determined not only in terms of the proportions of blastospores, hyphae and pseudohyphae, but also with regard to the mode of budding of blastospores and the positions of these particular cell types within the colonies. Hyphae with an atypical appearance and branching characters were observed both in regular-wrinkled and in irregular-wrinkled mutant colonies. Smooth colonies of the parental strain and the mutants exhibited the same hyphal network within the agar, suggesting that micro-environmental factors in the agar overcame the effects of these mutations.