Variability in the expression of two different cell surface carbohydrate determinants was examined with two agglutinating immunoglobulin M monoclonal antibodies (H9 and C6) and immunoelectron microscopy during growth of three strains of Candida albicans. A single strain of Candida parapsilosis did not express either antigen at any time during growth. Antigens were detected on the surface of C. albicans by agglutination tests with either H9 or C6 over a 48-h growth period. The difference in specificities of the monoclonal antibodies was demonstrated by Ouchterlony double-diffusion tests with solubilized antigens and by variabilities in the reactivity of the agglutinins among yeast strains. The antigenic determinants were isolated by specific immunoprecipitation and protease digestion and characterized by methods including high-pressure liquid chromatography, gas-liquid chromatography, and mass spectroscopy with both chemical and electron ionization. These determinants both contain mannose and glucose. In the case of antigen H9, an additional carbohydrate was detected with gas chromatography and mass spectroscopy. The location of antigens on individual cells was determined by indirect labeling of the determinants, first reacting cells with H9 or C6 followed by goat anti-mouse antibody conjugated with 20-nm colloidal gold particles. Transmission electron microscopy was used to examine cells. The antigens that were reactive with the monoclonal antibodies were associated with a flocculent surface layer. Expression of this layer and expression of the antigens is a dynamic process which is growth phase and strain dependent. The antigens were not expressed on very young cells and disappeared from the cell surface of most C. albicans strains with age. The use of monoclonal antibody to cell surface determinants may allow characterization of cell surface antigens of C. albicans and be helpful in establishing receptors which mediate adherence.