Collecting complete, timed stool samples for the estimation of faecal fat from infants wearing nappies is difficult. A gravimetric method has been adapted by applying a chloroform/methanol homophasic solvent system to extract lipids from whole soiled nappies. In a study of 22 collections in six infants, no stools were lost and the recovery of lipids was 96%, with results similar to a reference titrimetric method. In addition to total fat, individual lipids were measured using gas-liquid chromatography. The method simplifies stool collection and analysis, is aesthetically more acceptable, and leads to reduced microbial hazards. It also allows the detailed study of excreted lipid species enabling the coefficient of absorption of dietary lipids of various chain lengths to be determined individually.