Expressing serum organic toxicant concentrations per weight of total lipid rather than by volume of serum is often advantageous, but it requires a reliable and convenient method for determining the total serum lipids. We compared a completely enzymatic 'summation' method for estimating serum total lipids with a traditional gravimetric analysis. Serum total cholesterol (TC), nonesterified cholesterol (FC), triglycerides (TG), and phospholipids (PL) were assayed by automated, enzymatic methods and total lipids (TL) were calculated from the expression TL = 1.677 * (TC-FC) + FC + TG + PL. Examining three reference serum pools by both summation and gravimetric methods yielded results that agreed within 1-3%. The evaluation of thirty serum samples resulted in similar mean total lipid values (697 mg/dl gravimetric; 675 mg/dl summation) with excellent correlation between the two methods (r2 = 0.978). We conclude that the enzymatic summation procedure is a useful method for routinely estimating serum total lipid content.