Trehalase activity is markedly enhanced upon addition of glucose and a nitrogen source to cells of the fission yeast Schizosaccharomyces pombe. This increase corresponds to a post-translational activation of the enzyme, which is controlled by cAMP-dependent and cAMP-independent pathways. Recent work has shown that overexpression of SCK1 in Schiz. pombe is able to suppress mutations that result in reduced Pka1 (cAMP-dependent protein kinase A activity, suggesting that Sck1 (suppressor of loss of cAMP-dependent protein kinase) might be a functional analogue of Pka1 in the fission yeast. Here, an analysis of the possible role of Sck1 in the activation of trehalase triggered by glucose and a nitrogen source is reported in cells that were deficient in either Pka1, Sck1 or both protein kinases. The results showed that, except in repressed cells, Sck1 probably mediates a cAMP-independent activation of trehalase following the signal(s) triggered by glucose and the nitrogen source. The absence of functional Sck1 in depressed cells renders trehalase insensitive to activation by glucose and the nitrogen source even in the presence of Pka1, indicating that the Sck1-dependent, cAMP-independent pathway is the main signalling pathway controlling trehalase activation under derepression conditions. It is proposed that, during the activation of trehalase induced by glucose or a nitrogen source, the cAMP-Pka1 activation pathway previously characterized is to some extent parallel to this newly described one which includes Sck1 as phosphorylating enzyme. Neither of these two pathways, however, plays a key role in the heat-induced increase in trehalase activity.