The alpha-aminoadipate (AA) pathway for the biosynthesis of lysine was investigated in the wild type and in lysine auxotrophs of the fission yeast Schizosaccharomyces pombe. Of the eight enzyme activities of the AA pathway that have been examined so far, six were present in the extract of wild-type S. pombe cells. Growth response to AA and accumulation studies indicated that three lysine auxotrophs, the lys2-97, lys4-95, and lys8-1 strains, were blocked before the AA step and that four lysine auxotrophs, the lys1-131, lys3-37, lys6-3, and lys7-2 strains, were blocked after the AA step. Among the mutants investigated, the lys2-97 mutant exhibited an enzyme lesion at the cis-homoaconitate hydratase step, the lys1-131 and lys7-2 mutants exhibited lesions at the AA reductase step, and lys3-37 exhibited a lesion at the saccharopine dehydrogenase step. These results demonstrated the basic similarity of the AA pathway in S. pombe and Saccharomyces cerevisiae.