By selecting activities to complement Escherichia coli aro mutations, a gene responsible for the biosynthesis of aromatic amino acids in Schizosaccharomyces pombe (aro3) was cloned into pBR322. Three independent clones named pFNA1, pFNA2 and pFNA3 were obtained. pFNA1 could complement E. coli aroD only, whereas the other two plasmids were able to complement both aroD and aroE. The aro3 locus of S. pombe was found to be a gene cluster which can be subdivided into five complons, A through E (Strauss 1979). Transformation of S. pombe mutants defective in each complon with the pFNA plasmids indicated that pFNA1 carries at least a part of aro3A, the whole of B, C and D, as well as a part of E, whereas pFNA2 and pFNA3 carry a part of aro3C and the entire D and E complons. A physical map of the aro3 locus was constructed by analyzing the structure of these plasmids and their hybridization patterns to restricted genomic DNA. A transcript 4.5 kb long was detected as the sole aro3 mRNA encompassing all five complons. This study, in addition to the work of Strauss (1979), establishes that the arrangement of the aro3 complons in S. pombe in terms of their enzymatic coding activities is identical with that of Neurospora crassa, but different from that proposed for Saccharomyces cerevisiae.