Octylphenol was tested for acute toxicity to laboratory animals. Summary reports indicate oral administration of single doses of 5.0 g/kg as a 25% suspension in corn oil to 6 adult albino rats led to total mortality within 2 days post-treatment. Diarrhea, lethargy, and gastro-intestinal inflammation were observed. Single application of 2.0 g/kg undiluted test material under occlusion to clipped abraded or unabraded rabbit skin did not yield evidence of systemic toxicity; severe erythema and moderate edema were observed at treatment sites. Single instillation of 0.1 ml octylphenol into the right eyes of 6 albino rabbits led to severe corneal, iridial and conjunctival effects that persisted for 7 days post-treatment. Individual animal data are provided. Acute inhalation exposure (1 hour duration)of adult albino rats to a 45% (w/v) solution of octylphenol (116 mg/L concentation) in isopropyl myristate led to total mortality within 24 hours, respiratory distress and pulmonary hemorrhage. Exposure of 6 New Zealand albino rabbits to 0.5 g of test material introduced under occluded patch to closely clipped skin on the back and sides of the body for 4 hours led to slight erythema in 4 animals (mean primary irritation score of 0.2); all signs of irritation disappeared by 24 hours post-exposure, indicating octylphenol was not corrosive under the conditions of this test.