This study aimed to determine the effects of incorporating fish with 40%- or 30%-fat diets and the differences in response to fish or fish oil omega 3 fats. Men with high-normal blood pressure and elevated serum cholesterol were randomly allocated to one of seven diets for 12 wk. Fish or fish oil with a 40%-fat diet increased total cholesterol, HDL cholesterol, HDL2 cholesterol, and LDL cholesterol, and reduced triglycerides. The 30%-fat diet alone reduced cholesterol, LDL cholesterol, and HDL cholesterol, with triglycerides unchanged. Fish with the 30%-fat diet reduced cholesterol, LDL cholesterol, and triglycerides and increased HDL2 cholesterol. This study has shown that plasma lipids are affected similarly by fish or fish oil in men consuming a 40%-fat diet. Adverse effects of omega 3 fats on total and LDL cholesterol are reversed by a 30%-fat diet, whereas one daily fish meal substantially lowers triglycerides and reverses the fall in HDL cholesterol that is usual with a low-fat diet.