1. The effects of oral administration of Hilsa (Hilsa ilisa) fish oil (1 g oil/kg bodyweight per day) on the lipid profile, platelet aggregation, anti-oxidative status and glycaemic control of streptozotocin (STZ; 90 mg/kg bodyweight)-treated type 1 diabetic rats were compared with those in fish oil-treated or untreated non-diabetic rats. 2. After 3 weeks of fish oil feeding, plasma total cholesterol decreased in both the non-diabetic and diabetic rats by 35 and approximately 10%, respectively, and triglyceride fell by 69 and 20%, respectively, compared with control rats. 3. Fish oil feeding decreased non-esterified fatty acids (NEFA) by 29% in diabetic rats but the NEFA level in non-diabetic rats was unaffected. 4. In non-diabetic and diabetic rats, platelet aggregation decreased by 49 and 37%, respectively, and total anti-oxidant status increased by 18 and 17%, respectively, after fish oil feeding. 5. Insulin levels increased by 27% in the fish oil-fed non-diabetic rats, whereas insulin levels were markedly decreased in diabetic rats. Glucose levels were not altered at all and fructosamine levels decreased by 29% only in fish oil-fed diabetic rats. 6. The results of the present study suggest that Hilsa ilisa fish oil may ameliorate the atherogenic lipid profile, platelet hyperaggregation and the anti-oxidative defence of STZ-diabetic rats and the amelioration is thought to be independent of the effects of Hilsa on glycaemic control.