Cells of Schizosaccharomyces pombe disrupted in the tps1+ gene, which encodes trehalose-6P synthase, were unable to increase trehalase activity in response to the addition of glucose or nitrogen source. Moreover, in contrast to normal cells, Deltatps1 cells did not increase trehalase activity by heat shock. Overexpression of tps1+ in cells devoid of trehalose-6P synthase restored the ability to increase trehalase after addition of nutrients or by heat shock. In glucose-repressed cells, which are normally refractory to the activation of trehalase by glucose, overexpression of tps1+ enabled the cells to increase trehalase activity upon addition of the sugar. Northern hybridisations were used to determine the level of mRNA for trehalase in normal and Deltatps1 cells. Transcription for trehalase was not significantly altered upon addition of glucose or nitrogen source, but increased markedly in heat-shocked cells even though trehalase activity remained unchanged in Deltatps1 cells. These findings provide evidence for a role of trehalose-6P synthase in the signalling pathway causing post-transcriptional activation of neutral trehalase induced by nutrients or heat shock. However, trehalase increased in Deltatps1 cells under hypertonic conditions suggesting the existence in Schiz. pombe of a distinct regulatory mechanism for enhancement of trehalase, specifically triggered by osmostress.