Sera of 908 blood donors, average age 35 years, living in towns and villages of the Slovak Republic were tested for Toxocara canis antibodies using an ELISA-IgG test. The seroprevalence in the healthy population was estimated at 13·65%. Antibodies were predominantly demonstrated in the sera from persons living in rural communities (17·09%) compared to the sera investigated from urban communities (11·82%). Women had a significantly higher seropositivity than men. The serological response in 2703 sera from patients suspected of toxocarosis was compared with their clinical manifestation, sex and age. Toxocara antibodies were found in 27·41% of suspected patients. Although the seroprevalence in adults was significantly higher among women than men, in children, boys had a higher seroprevalence than girls. The main clinical manifestations were leucocytosis and eosinophilia (46%), ocular disorders (36%), lung, liver and neurological disorders (26%). The most severe forms of this disease were observed in 2 to 5-year-old children with geophagy.