Ninety-five percent of phospholipids (PLs) in bile is secreted as phosphatidylcholine or lecithin. The study of fatty acid patterns of phospholipids present in gallbladder bile could help clarify whether a preponderance of certain fatty acids could play a role in cholesterol gallstone formation in man. In acute bile acid-exchange experiments, it was found that more hydrophobic bile acids did promote the excretion in bile of PL rich in arachidonic acid (a prostaglandin precursor) and stearic acid. We studied, therefore, bile acid, cholesterol and phospholipid fatty acid patterns (measured by gas chromatography) in gallbladder bile, obtained by duodenal intubation and cholecystokinin-stimulation of 24 healthy volunteers with normal liver/gallbladder function (ultrasound). PL-fatty acid composition (mean % +/- SD) was 41.40 (+/- 1.41) for palmitic acid, 2.68 (+/- 0.82) for palmitoleic acid, 5.50 (+/- 1.55) for stearic acid, 12.09 (+/- 0.98) for oleic acid, 32.83 (+/- 3.04) for linoleic acid and 5.64 (+/- 1.59) for arachidonic acid. The proportion of biliary deoxycholate was positively correlated with arachidonic acid (r = 0.71; p less than 0.01), whereas chenodeoxycholate was inversely correlated with arachidonic acid (r = -0.53; p less than 0.01). There was a positive correlation between biliary chenodeoxycholate and linoleic acid (r = 0.48; p less than 0.05) and a negative correlation between biliary deoxycholate and linoleic acid composition (r = 0.68; p less than 0.01). Also a correlation was found between palmitic acid and cholesterol saturation index (r = 0.49; p less than 0.05). We conclude that the hydrophobic bile acid deoxycholate, which does not desaturate cholesterol in bile, promotes the biliary excretion of arachidonic acid. Since arachidonic acid could induce the gallbladder mucosa to produce prostaglandins and mucus, increased biliary PL-arachidonic acid composition might be a factor in cholesterol gallstone disease.