Receptors for the two peroxisomal targeting signals PTS1 and PTS2 have recently been identified in yeasts. The disparate subcellular locations of PTS receptor homologs have led to proposals of receptor shuttling between the cytosol and the peroxisomal membrane, and to the suggestion that some of these molecules may even reside normally in the peroxisomal matrix. A peroxisomal membrane protein that interacts with the PTS1 receptor in Saccharomyces cerevisiae may serve as the receptor-docking site on the organelle. The conservation of the PTS1 receptor in several yeasts has led to the cloning and characterization of the gene encoding its human homolog, PTS1R, which is mutated in a group of patients afflicted with fatal peroxisomal disorders. The identification of peroxisome assembly genes in yeasts is likely to lead to the cloning of additional human genes responsible for other generalized peroxisomal disorders. Protein unfolding is not a prerequisite for import of peroxisomal matrix proteins, suggesting novel mechanisms for the translocation of polypeptides across the peroxisomal membrane.