All of the enzymes involved in the β-oxidation pathway were identified from juvenile and adult postparasites of the mermithid nematode Romanomermis culicivorax. The postparasites readily took up exogenous [14C-U]palmitate and oxidized it to CO2, indicating that the β-oxidation pathway is functional. The extent to which this pathway is utilized during the natural cycle of the nematode is discussed.