The proliferation of peroxisomes was observed in Saccharomyces cerevisiae MT8-1 cells grown in a medium containing 0.5% oleic acid and 0.1% glucose as the carbon sources, together with the induction of peroxisomal enzymes, such as catalase and acyl-CoA oxidase. The results of the subcellular fractionation and Western blot analysis indicated that Candida tropicalis peroxisomal isocitrate lyase (ICL) highly expressed in S. cerevisiae under the activation of the GAL7 promoter (Oda et al., Arch. Microbiol., 156, 439-443, 1991) was partially transported in the particulate fraction containing peroxisomes and mitochondria. Furthermore, observation under immunocytochemical electronmicroscopy revealed that the enzyme protein was at least partially localized inside peroxisomes proliferated in S. cerevisiae, but not in mitochondria. These facts indicated that the peroxisomal targeting signal of C. tropicalis ICL seemed to be able to function in S. cerevisiae, but that the ICL expressed was not sufficiently accommodated into peroxisomes, probably due to the overproduction of the enzyme protein for S. cerevisiae peroxisomes.