Peroxisomes are ubiquitous eukaryotic organelles. The proteins required for peroxisome biogenesis are called peroxins, and mutations in the peroxin genes cause the devastating human developmental syndromes called the peroxisome biogenesis disorders. Our interest is in elaborating the roles that peroxisomes play in Caenorhabditis elegans development, and in establishing an invertebrate model system for the human peroxisome biogenesis disorders. The genome of C. elegans encodes homologs of 11 of the 13 human peroxins. We disrupted five nematode peroxins using RNA interference(RNAi) and found that RNAi knockdown of each one causes an early larval arrest at the L1 stage. Using a green fluorescent protein reporter targeted to the peroxisome, we establish that peroxisomal import is impaired in prx-5(RNAi) nematodes. prx-5(RNAi) animals are blocked very early in the L1 stage and do not initiate normal postembryonic cell divisions,similar to starvation-arrested larvae. Cell and axonal migrations that normally occur during the L1 stage also appear blocked. We conclude that peroxisome function is required for C. elegans postembryonic development and that disruption of peroxisome assembly by prx-5(RNAi)prevents scheduled postembryonic cell divisions. Defects in the cellular localization of peroxisomal proteins and in development are shared features of human and nematode peroxisome biogenesis disorders. In setting up a C. elegans model of peroxisomal biogenesis disorders, we suggest that genetic screens for suppression of the Prx developmental block will facilitate identification of novel intervention strategies and may provide new insights into human disease pathogenesis.