The results of a tiral using chenodeoxycholic acid in 400 patients with cholesterol gallstones are reported. The "qualifying points" of such treatment are compared with the literature data in clinical and laboratory terms. 54% of 300 in clinical and laboratory terms. 54% of 300 patients who received less than 12 mg/kg/day achieved dissolution in a mean time of 11 months, while 64% of the remainder (12-15 mg/kg/day) did so in an average of 8 months. Microcalculi proved most sensitive to treatment (65% of positive results). Lithiasis over 5 years standing and over-weight (10% over the ideal figure) were factors that imposed more protracted treatment. Careful selection of candidates was proved important by the results of quarterly liver and intestine performance examinations. These were more extensive and more clearly aimed than those proposed by other workers. They showed that the acid is neither hepato nor enterotoxic. Indeed, no serious side-effects were noted.