The lithogenic character of human gallbladder bile was investigated by a mathematical model on the basis of a clinical data set. Each bile was described by means of the quaternary system bile salts--phospholipids--free fatty acids--cholesterol. Reporting a set of bile samples on the tetrahedron of concentrations, a clear separation emerged between the control bile, the bile from patients with gallstones, and the bile of subjects with gallbladder dyskinesia. This group was characterized by a largely increased content of free fatty acids.