Published work from the first author's laboratory is discussed. The previously estimated molar ratios between total bile salts (TBA) and cholesterol (C) and between lipid-soluble P (P) and cholesterol in gall bladder bile of young hamsters, mice and chicks reared on different diets were compared with the recently established limits for solubility of C in aqueous solutions of suitable bile salts and lecithin. When total phospholipids (P) were considered equal to lecithin, the molar ratios TBA: C and P: C corresponded to saturation or supersaturation when the prevalence of cholesterol gall stones was high, and to unsaturation when the prevalence was low, in the following cases: abundant occurrence of C stones in hamsters on a diet with 74.3% glucose and no added fat; absence of C stones in hamsters on a diet with 74.3% rice starch and no added fat; absence of C stones in hamsters on a diet with ground polished rice 28.3, dry yeast 36 and lard 10% and a trace of cupric sulfate; absence of stones in hamsters on stock diet; low prevalence of C stones in hamsters on a diet with 3% filtrol-treated cod liver oil; low prevalence in hamsters on a diet with 10% fat from a margarine rich in linoleic acid; absence of C stones in mice and chicks. The molar ratios TBA: C and P: C were not in accord with the prevalence of C stones in the following cases: low prevalence of C stones in hamsters on a diet with 74.3% lactose and no added fat, where the ratios corresponded to moderate supersaturation; C stones in hamsters on a diet with glucose 62.3 and rice starch 12% with no added fat but small amounts of cupric sulfate, manganous sulfate and potassium iodide, where the ratios corresponded to unsaturation in bile from most animals having stones; occurrence of C stones on a diet with glucose 52.3, rice starch 12 and butterfat 10%, where the ratios corresponded to unsaturation. Ratios corresponded to supersaturation in bile from most patients with gall stones rich in C and a functioning gall bladder, or from patients with peptic ulcers but normal liver and biliary tract.