Somatostatin and its long-acting analogue SMS 201-995 (Sandostatin) have been suspected of causing steatorrhoea. The aim of this study was to examine the effect of SMS 201-995 on fat assimilation in healthy subjects, using 14C-triolein and 3H-oleic acid as tracers of dietary triglycerides and free fatty acids, respectively, and 51CrCl3 as non-absorbable marker. Six healthy male volunteers participated in the double-blinded, randomized, crossover study. In each test period either 1 ml of SMS 201-995, containing 200 micrograms, or 1 ml of isotone saline was given subcutaneously three times within 16 h. Faeces were collected for 3 days, every stool separately. The faecal 14C-triolein and 3H-oleic acid excretion was calculated from two aliquots of faeces. In addition, the mean daily faecal fat excretion was estimated. When placebo was given, the median 14C-triolein excretion was 1% (range, 0.9-1.6%), the median 3H-oleic acid excretion was 5% (range, 3-10%), and the daily faecal fat excretion was 4 g/day (range, 1-6 g/day), all within normal limits. When SMS 201-995 was given, the faecal 14C-triolein excretion increased to a median of 75% (range, 43-119%), the 3H-oleic acid excretion increased to a median of 82% (range, 46-126%), and the faecal fat excretion increased to a median of 22 g/day (range, 4-34 g/day), all clearly above normal. The faecal 14C-triolein/3H-oleic acid test showed triglycerides and free fatty acids to be equally malassimilated, which indicates malabsorption.