The cytoplasmic ribosomal proteins from a fission yeast Schizosaccharomyces pombe were analysed by two-dimensional polyacrylamide gel electrophoresis. Seventy-three protein species were identified in the 80S ribosome, and named SP-S1 to SP-S33 and SP-L1 to SP-L40 in the small and large subunits, respectively. Many of these proteins could be correlated to those of Saccharomyces cerevisiae on the basis of their electrophoretic mobilities. Eleven proteins were isolated from the 80S ribosome, and their amino acid compositions were determined. Of these, SP-S6, SP-L1, SP-L12, SP-L15, SP-L17, SP-L27, SP-L36 and SP-L40c and d were sequenced from their amino-termini. SP-S28 and SP-L2 appear to have their amino-termini blocked. These results were compared with the data available for the S. cerevisiae and rat liver ribosomal proteins. The S. cerevisiae counterparts of the eight proteins mentioned above were found to be YS4, YL1, YL10, YL14, YL35, YL40 and YL44c and d, respectively. The rat liver counterparts of SP-S6, SP-L1, SP-L27 and SP-L40c and d were the rat S6, L4, L37 and P2, respectively. Comparison of the partial sequences of these ribosomal proteins suggests that these two yeasts are relatively far apart, phylogenetically.