The changes in the composition of bile can lead to the process of it's crystallization in the gallbladder. In bile model it was shown that inflammation with the generation of reactive oxygen metabolites may induce and influence the cholesterol monohydrate crystal formation within supersaturated bile. The aim of this study was to investigate the ability to detect traces of reactive oxygen metabolites, thiobarbituric acid reactive compounds and dien, in order to compare cholesterol and bilirubin contents in bile and serum during different conditions of inflammation in the gallbladder's wall. In every bile sample a reference to free radical reaction was found. There was an increase in MDA during higher degree of inflammation in the gallbladder, but no alteration in the dien content was observed. In case of common bile duct stones the bilirubin in the serum and in the gallbladder was parallelly high, but in other cases there were no significant correlation. In an occluded gallbladder with hydrops the content of protein was significantly higher in 85% of the cholesterol stones. As a conclusion, free radical reactions in the wall of gallbladder as well as in bile can induce gallstone formation. Further studies are needed to clarify the time which is sufficient to change the composition of bile and the degree of inflammation which lead to the onset of stone formation.