A micromethod involving "high-performance" lipid chromatography was developed for determining cholesterol in sera obtained from animals that has been infused with high doses of lipid emulsions. Only 50 micro L of serum is required, and there is no interference from turbidity, bilirubin, fat-soluble vitamins, and sterols. Correlation with the commonly used Abell-Kendall method was good at cholesterol concentrations as great as 10.0 g/L (r = 0.998). The assay is ideal for determinations on samples from pediatric and hyperlipidemic patients. It is particularly useful for monitoring patients on lipid-emulsion therapy and for toxicological studies with small animals.