Genetically heterothallic strains of various sterile mutants were assayed for residual production of the corresponding mating pheromone as well as responsiveness towards the opposite pheromone. No sexual activities were detected in ste11 strains (previously referred to as aff1 or steX, which we show are allelic), whilst the production of M factor was unaffected by ste1 to ste10 mutations. P factor production was still possible in class I ste mutants (ste5, ste6 and ste10), which also allow meiosis in diploid strains. With the exception of the leaky ste10-F23 mutant, no changes in cell morphology were induced by exposure to the opposite pheromone in the ste mutant strains.