Alpha-L-fucosidase (ALF), AST, ALT and GGT activities were measured in blood serum of 36 patients with recurrent cholelithiasis (group I), 32 patients with ductal and/or bladder cholelithiasis (group II), 24 patients with focal changes in the liver (group III) and in 22 patients without disturbances of gastrointestinal tract (control group). A statistically significant increase in ALF activity was found in the patients with recurrent cholelithiasis as compared to the control group (p < 0.001), the patients of group II (p < 0.001) and the patients of group III (p < 0.05). The AST and ALT activities were higher both in group I and in group II than in the control group (p < 0.001 and p < 0.02 for group I and group II, respectively), whereas the mean GGT activity was significantly higher in all three patients groups as compared to the control group (p < 0.001 in all cases). On the basis of the observed differences in the activities of the enzymes studied it was postulated that the determination od ALF activity in blood serum of patients with cholelithiasis may provide the means for early diagnosis of the predisposition to recurrent stones.