The Saccharomyces cerevisiae ADR1 gene has recently been demonstrated to control transcription of several genes encoding peroxisomal proteins or proteins necessary for peroxisome formation. Therefore, the effect of two other genes (SNF1 (CAT1, CCR1) and SNF4 (CAT3)) known to control derepression of glucose-repressible genes was studied. Levels of transcripts of genes encoding catalase A, fatty acid beta-oxidation enzymes and of the PAS1 gene are reduced in snf1 and snf4 mutants on ethanol as well as on oleic acid medium. By immunogold labelling with an antibody directed against peroxisomal thiolase, clusters of peroxisomes were detected in wild-type cells, whereas smaller single peroxisomes were observed in adr1 mutant cells. Results of immunofluorescence experiments are consistent with these observations. No peroxisomes were detected in snf1 and snf4 mutants by immunogold labelling as well as by immunofluorescence.