A precise analysis for the identification of the yeast genus Schizosaccharomyces by immunoenzymatic methods is presented. By use of the murine monoclonal antibody JHF13-17, two proteins were recognized in cell extracts of S. pombe, S. malidevorans, and S. japonicus in Western blot analyses and were termed SSP-A and SSP-B (Schizosaccharomyces-specific proteins). The migration pattern of the proteins was identical in 18 strains of these species that were tested. An analogous protein doublet was also visualized in cell extracts of ten strains of S. octosporus, and, owing to the migration pattern, these proteins were termed SSP-B and SSP-C. A polyclonal antiserium raised against the SSP-A and SSP-B from S. pombe cross-reacted with SSP-A and SSP-B from S. malidevorans and S. japonicus and SSP-B and SSP-C from S. octosporus.