We demonstrate that a diffusible factor is secreted by h cells of the fission yeast Schizosaccharomyces pombe, whose mating pheromones have not been described. This factor, tentatively named the h-factor, affects hS. pombe cells and induces their elongation under nitrogen-depleted conditions. Circumstantial evidence suggests its physiological significance in the mating process. Despite their sterility, hras1 cells secrete this factor. However, hras1 cells have apparently lost the ability to respond to it. This may suggest that the gene product of S. pombe ras1, a homologue of mammalian ras oncogenes, is involved in the mechanism for responding to mating pheromones.