The prevalence of cholesterol gallstones differs among inbred strains of mice fed a diet containing 15% (wt/wt) dairy fat, 1% (wt/wt) cholesterol, and 0.5% (wt/wt) cholic acid. Strains C57L, SWR, and A were notable for a high prevalence of cholelithiasis; strains C57BL/6, C3H, and SJL had an intermediate prevalence; and strains SM, AKR, and DBA/2 exhibited no cholelithiasis after consuming the diet for 18 weeks. Genetic analysis of the difference in gallstone prevalence rates between strains AKR and C57L was carried out by using the AKXL recombinant inbred strain set and (AKR x C57L)F1 x AKR backcross mice. Susceptibility to gallstone formation was found to be a dominant trait determined by at least two genes. A major gene, named Lithl, mapped to mouse chromosome 2. When examined after 6 weeks on the lithogenic diet, the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (EC 1.1.1.88) was downregulated as expected in the gallstone-resistant strains, AKR and SJL, but this enzyme failed to downregulate in C57L and SWR, the gallstone-susceptible strains. This suggests that regulation of the rate-limiting enzyme in cholesterol biosynthesis may be pivotal in determining the occurrence and severity of cholesterol hypersecretion and hence lithogenicity of gallbladder bile. These studies indicate that genetic factors are critical in determining gallstone formation and that the genetic resources of the mouse model may permit these factors to be identified.Both atherosclerosis and cholelithiasis result from excess cholesterol; in the one case cholesterol is deposited in arterial walls, and in the other case cholesterol precipitates in the gallbladder. Both diseases are prevalent in cultures consuming a Western diet, and both can be induced in animal models by a diet high in cholesterol (1,2). In Western cultures, heart disease is the major cause of death, and gallstone disease is present in 10-40% of individuals over the age of 60 (3).Genetic factors apparently play an important role in the development of cholesterol gallstone disease. Among studies of gallstone formation in animals, Alexander and Portman (4) demonstrated that C57BL/6 mice are susceptible to cholelithiasis, but CBA mice are resistant. In both strains bile was supersaturated with cholesterol but not to the same degree (4). Fujihara et al. (5) reported that the prevalence of gallstones varied from 0% to 100% among six strains of laboratory mice.Evidence for the importance of genetic factors in human cholelithiasis is limited. Gallstone disease can be familial (6-11), and the bile from healthy sisters of female gallstone patients is more lithogenic than controls (11,12). In certain native populations of North and South America, a high percentage of adults develop cholesterol gallstones, suggesting common genetic factors (13,14).In previous studies, high fat plus high cholesterol diets produced atherosclerosis and gallstones in some strains of mice (15). In this report, we survey common inbred strains of mice for susceptibility to cholelith...