Kinetic experiments with synchronously sporulating cultures of a homothallic h90 strain of Schizosaccharomyces pombe showed that trehalase activity abruptly increased in the late sporulation process, coinciding with the appearance of visible spores. Trehalase activity was absent in vegetative cells. A set of strains different in genetic constitution at the mating type loci was tested for induction of trehalase on nitrogen-free sporulation medium. The appearance of trehalase activity on the sporulation medium was observed only in sporulating cultures; cultures of homothallic strains (h 90) and diploid strains heterozygous for mating type (h +/h-), and mixed cultures of heterothallic h+ and h- strains. Trehalase activity was not induced in nonsporogenic strains: heterothallic haploid strains (h+ and h-), diploid strains homozygous for mating type (h+/h+ and h-/h-) and the homothallic strain harboring the mutation in the mat2 gene, which was unable to undergo the first meiotic division. Trehalose accumulation on the sporulation medium was observed solely in the sporulating cultures. These results led us to conclude that the induction of trehalase activity as well as the accumulation of trehalose in the medium lacking nitrogen sources was a sporulation-specific event under the control of the mating type genes.