Peroxisome induction can be expressed as an increase in peroxisome area (proliferation) or as an increase in peroxisomal fatty acid oxidation (activity). This study compares proliferation and activity as endpoints for hepatic peroxisome induction by perfluorodecanoic acid (PFDA). Fluorocarboxylic acids such as PFDA represent a class of compounds possessing commercially important surfactant properties. A single 50 mg/Kg ip. dose of PFDA produces a characteristic “wasting syndrome” in male F-344 rats. Symptoms include hypophagia, weight loss, hepatomegaly, and delayed lethality. Hepatic studies reveal changes similar to those seen with the hypolipidemic agent clofibrate. These include mitochondrial disruption, endoplasmic reticulum and peroxisome proliferation, and increased peroxisomal acyl-CoA oxidase activity.Male Fisher-344 rats received a single ip. dose of 2, 20, or 50mg/Kg PFDA dissolved in 1:1 propylene glycol/water and were sacrificed 8 days post-dose. All control rats received an equal volume of vehicle ip. Animals were provided food and water ad libitum, except pair-fed controls which received the same restrictive food intake consumed by their weight-paired dosed partners (50mg/Kg PFDA group) to simulate the hypophagia associated with PFDA.