Uptake and esterification of fatty acids from micellar lipid solutions by human small intestinal mucosa was studied in vitro. Small bowel biopsies, obtained during endoscopy, were incubated at 37 C in RPMI 1640 medium containing various concentrations of micellar lipids (sodium taurocholate, oleate and monoolein). Oleate uptake from the micellar solution was enhanced and correlated positively with micellar ingredient concentration at a range of 2.4 to 9.6 mmol/l taurocholate. Triglyceride (TG) synthesis during incubation was affected by micellar bile salt concentration, as well as by micellar concentration of oleate and monoolein. At a high concentration of bile salt, TG synthesis was decreased. Boiling of tissue specimens resulted in complete inhibition of TG synthesis, but did not affect oleate uptake. When intestinal biopsy tissue was incubated in a micellar lipid solution and subsequently organ-cultured, gradual depletion of tissue oleate and TG content was evident, concomitant with TG secretion to the medium. TG secretion persisted during 24 h of organ culture, but decreased with time. Intestinal TG synthesis was not affected by methylprednisolone, pentagastrin, nicotinic acid or insulin, but was decreased by cimetidine.