Peroxisomes are essential organelles that rid cells of toxic substances such as hydrogen peroxide. Peroxisomal disorders are characterized by widespread organ pathology, including neurodegeneration. The genetic basis of many of these is known, but how the various mutations cause disease remains unclear. Denis Crane and co-workers have been investigating Zellweger syndrome (ZS) and D-bifunctional protein (D-BP) deficiency, two peroxisomal disorders characterized by formation of small numbers of over-sized peroxisomes. They report that these characteristics, and also altered cytoplasmic peroxisomal distribution, reflect defects at different stages of microtubule-mediated peroxisome division and trafficking (see p. 636). The authors have examined peroxisomes and microtubules in fibroblasts from patients with ZS or D-BP deficiency and studied the effects of overexpression of PEX11β, a peroxisomal membrane protein implicated in peroxisome proliferation and division. Overexpression of PEX11β restores the abundance, cytoplasmic distribution and alignment of the peroxisomes along microtubules. This suggests that peroxisome proliferation and division, and binding of peroxisomes to microtubules are mechanistically linked processes. The researchers speculate that oxidative damage caused by regional loss of peroxisomes may be responsible for the neurodegeneration seen in ZS and D-BP deficiency.