We tested whether cultured human jejunal mucosa incorporates fatty acid into esterified lipids and whether organ culture can serve as a model system to study lipoprotein secretion by the human gut. Jejunal biopsies obtained from seven subjects were cultured for 24 h in medium containing 2 microCi of [3H]palmitic acid. More than 95% of the radioactivity incorporated by the tissue was found to be associated with esterified lipids: triglycerides, cholesterol esters and phospholipids, 7 . 8 +/- 1 . 2, 0 . 5 +/- 0 . 1 and 14 . 0 +/- 1 . 5 nmol/10 mg weight respectively. During the culture labelled triglycerides, phospholipids and cholesterol esters were secreted to the medium. Most of the newly synthesized esterified lipids in the medium were found in the d < 1 . 019 g/ml and d = 1 . 019--1 . 063 g/ml fractions. The majority of the newly synthesized triglycerides were found in the d < 1 . 019 g/ml fraction. Labelled cholesterol esters were enriched in the d = 1 . 063--1 . 21 g/ml fraction. Boiled biopsies adsorbed negligible amounts of radioactive palmitic acid and did not synthesize esterified lipids. The addition of puromycin to the culture medium and preincubation with colchicine resulted in decreased uptake of the labelled fatty acid and decreased secretion of esterified lipids to the medium. These experiments indicate that cultured human intestinal mucosa is a suitable model to study lipid synthesis and lipoprotein secretion by the human intestine.