Recent data from studies of peroxisome assembly and the subcellular sorting of peroxisomal matrix and membrane proteins have led to an expansion of the 'growth and division' and 'endoplasmic reticulum-vesiculation' models of peroxisome biogenesis into a more flexible, unified model. Within this context, we discuss the proposed role for the endoplasmic reticulum in the formation of preperoxisomes and the potential for 15 Arabidopsis peroxin homologs to function in the biogenesis of peroxisomes in plant cells.