Peroxisomes (microbodies) have a long evolutionary lifespan, but in cell biology they are still young. It is gratifying to see that most recent advances in our knowledge of peroxisomes come from quite different disciplines, ranging from molecular biology and cell biology to clinical research. The identification in terms of cDNA sequences of enzymes, the localization in terms of immuno-electron microscopy, and the cell biological aspects of the organelle biogenesis have seen substantial progress very recently. Likewise, the phenomenon of peroxisome proliferation induced by a number of drugs,...