ABSTRACT The test material@ API 78-7@ #6 Heavy Fuel Oil (API Gravity 17.1/0.8%S)@ was tested for potential acute toxicity@ using a battery of six tests: Primary Skin Irritation@ Primary Eye Irritation@ Skin Sensitization@ Acute Dermal Toxicity@ Acute Oral Toxicity@ and Subacute Dermal Toxicity. Materials@ methods@ and results of individual tests are presented in this report. The test material API 78-7 produced slightly irritating primary skin effects. The acute dermal irritation but also obvious treatment-related signs at the 8 ml/kg dosage level; histopathologic examination of tissues confirmed dermal and hepatic toxicity at that dosage level. The oral median lethal dose@ i.e.@ oral LD50@ of the test material is greater than 25 ml/kg. The test material was minimally irritating for primary eye irritation. Results of the skin sensitization test indicate that API 78-7 is mildly sensitizing.