Candida albicans is an opportunistic pathogen which may give rise to superficial and systemic infections. In the present study, C. albicans adhesion was studied by expression of C. albicans DNA sequences encoding adhesion functions in a nonadherent strain of Saccharomyces cerevisiae. Adherent transformant cells of S. cerevisiae harbouring a C. albicans genomic library cloned in a yeast-Escherichia coli shuttle vector were selected by using tissue culture-treated polystyrene as the attachment substratum. One transformant exhibited enhanced adhesion to treated and untreated polystyrene as well as autoaggregation, unlike control cells bearing the vector alone. Analysis of this clone revealed an insert of ca. 4.5 kb from C. albicans. Curing of the plasmid resulted in loss of adhesion and autoaggregation properties. A subclone bearing a reduced insert of 3.3 kb retained the ability to autoaggregate, to bind to treated and untreated polystyrene, and to adhere to buccal epithelial cells, unlike appropriate controls. Further subcloning of the insert to 2.7- and 1.9-kb fragments resulted in incremental decreases in adhesion and autoaggregation, whereas smaller fragments did not confer these properties. Hybridization of the 2.7-kb segment with C. albicans and S. cerevisiae DNA confirmed its origin as a single-copy sequence in the C. albicans genome as well as the absence of a homologous sequence in the genome of S. cerevisiae. The data suggest that the adhesion and aggregation phenomena of the transformant cells are related to expression of a C. albicans surface antigen encoded by the cloned DNA fragment.