THE QUANTITATIVE fecal fat determination is an important laboratory procedure in studying intestinal malabsorption. It establishes the presence and measures the degree of malabsorption of fat, and it may be used to evaluate the efficacy of treatment. Methods The survey covers 149 patients who were studied as inpatients or outpatients at the Gastrointestinal Clinic of the Hospital of the University of Pennsylvania from 1962 to 1966. All had ingested standard diets containing 90 to 100 gm of fat per day. More than 90% of the determinations were done on a 72 hour or longer stool collection. More than one fecal fat determination was frequently done on each patient, but for this report, only the first determination was used. The method of Van de Kamer et al1 was employed for quantitative fecal fat determination. More than 5 gm of fecal fat and more than 200 gm net weight of stool