The aim of this study is to determine if fat in the duodenum affects gallbladder contraction and plasma cholecystokinin. We evaluated the effect of intraduodenal(I.d.) lipomul on plasma concentration of cholecystokinin-like immunoreactivity(CCK-LI) and gallbladder(GB) contrac- tion in 8 human volunteers. In addition, effects of atropine on plasrna CCK-LI and GB contrac- tion were studied. GB contraction was calculated by measuring GB volume by serial ultrasonograms and expressed as % of the basal volume. Whereas iv saline failed to influence either plasma CCK-LI or GB volume, lipomul in 3 different doses(0.25, 0.5, 1.0ml/kg) pro- duced significant increases(P<0.05) in plasma CCK-LI and significant decreases(P<0.05) in GB volume during a 90 min period of observation. However, the responses of CCK-LI and GB volume were not dose related. Atropine sulfate given iv, 15ug/kg/hr, inhibited lipomul induced GB contraction during the first 15 min which was followed by a partial contraction(not signif- icant). No significant effect of atropine on plasma CCK-LI was apparent also. Thus we con- clude that lipomul produced significant increases in contraction of GB and plasma CCK-LI. The peak concentration of CCK-LI coincided with the rnaximum GB contraction. Atropine did not significantly influence lipomul-stimulated GB contraction and did not influence plasma CCK-LI. Thus no significant cholinergic effect was apparent. (Korean J Gastroenterol 1994; 26: 675 682)