These studies were undertaken to test the hypothesis that interfacial resistance may be an important rate-limiting factor in cholesterol gallstone dissolution. The addition of lincomycin hydrochloride to the gallbladder bile of dogs in an in vitro bath system resulted in an acceleration in the rate of dissolution of a compressed cholesterol monohydrate pellet incubating in the bile. However, the constant infusion of lincomycin for 13 d directly into the gallbladders of conscious, unrestrained dogs, which resulted in biliary lincomycin concentrations comparable to that of the in vitro tests, did not alter the dissolution rate of a compressed cholesterol monohydrate pellet which had been surgically placed into the gallbladder. We therefore conclude that the interfacial resistance between the cholesterol monohydrate pellet and the bile may be reduced by the addition of lincomycin to the gallbladder bile which, in the in vitro environment, results in an acceleration in the rate of dissolution of compressed cholesterol pellets. However, the ineffectiveness of lincomycin in accelerating the dissolution of cholesterol pellets in vivo suggests that interfacial resistance is not the only rate-limiting factor in gallstone dissolution. Other factors, such as mixing, may also be critical.