The relationship between giardiasis and ABO blood groups was studied in a group of 136 children from Eastern Slovakia, with a special attention to ethnic specifics of gipsy children. The study showed no statistically significant differences in the distribution of ABO blood groups between the subgroup of Giardia-infected gipsy children and the gipsy population minority living in the area. On the other hand, the ABO distribution pattern in subgroup of non-gipsy children infected with Giardia intestinalis was found to differ from that in the general non-gipsy Eastern Slovakian population by the absence of blood group AB among children with giardiasis. There was indicated a tendency towards an increased frequency of blood group B in subgroup of Giardia-infected gipsy children and towards group A in subgroup of nongipsy children with giardiasis, but the differences were not statistically significant.