Quantitative incorporation and esterification of (9–10) 3H palmitate into jejunal mucosa was studied in vitro comparatively on human biopsies and on everted rings of rat intestine following various incubation times. This procedure is fitted for investigation of the glycerophosphate pathway. Quantitatively the total uptake of palmitate was similar in man and rat. But the distribution among the various esterified fractions was different in animal and man and different again in coeliac disease. Notwithstanding incorporation of palmitate into triglyceride the fatty acid composition of mucosal triglyceride showed little or no modificatio