A newly synthesized inhibitor of pancreatic lipase and micelle formation, FL-386, was administered at a dose of 400 mg (in the diet, for seven consecutive days) to nine healthy adult volunteers, and changes in faecal mass, frequency of defaecation, and properties of the stools were observed. High performance liquid chromatography and gas-liquid chromatography were used to analyse the faeces for short-chain carboxylic acids, neutral sterols, bile acids, fats and hydroxyfatty acids. FL-386 had little effect on the amounts and composition of short-chain carboxylic acids, neutral sterols, and bile acids excreted, nor did it produce changes in the composition of fatty acids, or the percentages of hydroxyfatty acids in the stool. However, in those patients treated with FL-386, the faecal mass was increased, and stools were softer and contained increased amounts of fatty acids. The compound did not produce particularly fatty stools. It was concluded that FL-386 induces slight disturbance in the digestion and absorption of dietary lipids.