The ras1 gene, an oncogene homologue, is known to be essential for recognition of the mating pheromone and hence for conjugation but not for vegetative growth in Schizosaccharomyces pombe. To facilitate further characterization and genetic manipulation of this gene, we have mapped it by using S. pombe strains which carry the Saccharomyces cerevisiae LEU2 gene inserted next to ras1 on the chromosome. Crosses with tester strains revealed that ras1 is tightly linked to pro2 on chromosome I. Furthermore, we have shown that ras1 is allelic with ste5, one of the sterility genes described by O. Girgsdies. The map position previously reported for ste5 eventually turned out to be false.