Spectrin is the principal component of a system of structural proteins that are associated with the plasma membrane cytoplasmic surface. Its structure and function has been best characterized in mammalian erythrocytes (1). Proteins related to the a- and b-erythrocyte spectrin have been detected in almost all vertebrate tissues, and also in plants (2) and hyphal fungae (3). We studied spectrin-like proteins in budding yeasts Saccharomyces cerevisiae and fission yeasts Schizosaccharomyces japonicus var. versatilis. Western blot analysis using anti-chicken and anti-human erythrocyte spectrin antibodies was used for spectrin immunodetection. Band at 220 kDa in cells and protoplasts extracts of both yeast strains was detected. Additional bands were present at 50, 34 and 20 kDa in S. cerevisiae, and 44, 34 and 20 kDa in Sch. versatilis. Fluorescence microscopy revealed distinct labelling of the spectrin-like antigens at the cell surfaces and in vacuolar membranes of cells and protoplasts of both yeast species. In addition, the antigens were spread in the cytoplasm of both cells as fluorescent patches and as a diffuse fluorescence in Sch. versatilis nuclei. In mating and sporulating cells spectrin-like antigens lined the cell surface and prespore membranes. Electron microscopy of immunogold labelled cells and protoplasts revealed spectrin-like antigens in the cell wall, plasma membrane, ER, vacuole, nuclei, vesicles and mitochondria. Contrary to plant and some other fungal cells, spectrin in yeasts did not co-localize with actin. Growing regions of the cells were not preferentially labelled. Spectrin antigens correlated with actin only in protoplasts and maturing spores where patches of both lined the whole surface.