Toxocarosis is a zoonotic disease caused by migration and subsequent localization of nematode larvae of Toxocara spp. in human organs and tissues, which is manifested with development of various non-specific clinical symptoms. Main diagnostic methods are serological and consists in proving the presence of anti-Toxocara IgG antibodies in patient's sera. In humans, anti-Toxocara IgG has been shown to persist in the serum for a long time and cannot be used to distinguish between past and recent infection. Aim of the present work is to investigate the diagnostic significance of the specific IgG avidity level, determined by an immuno enzyme test developed by us, and the presence of anti-Toxocara IgA for distinguishing between acute and chronic toxocarosis. The study included 130 patients with positive results in routine serological ELISA and Western blot tests and with clinical symptoms of visceral and ocular toxocarosis. The results revealed low IgG avidity (≤40%) in nine (7.3%) and presence of anti-Toxocara IgA antibodies in 36 (26.2%) of the subjects. Low avidity of IgG antibodies was found only in the first tests, and a presence of specific IgA for up to 9 months. The results of our study give us reason to believe that determination of the IgG avidity in toxocarosis is of greater diagnostic value than the presence of IgA to establish the stage of the disease. Display omitted •The main methods of diagnosing the human toxocarosis is serological.•The diagnosis of the recent infection is difficult.•ELISA IgG and Western blot, cannot distinguish past from recent infection.•Specific IgA antibodies persist for up to 9 months after infection.•Low avidity of specific IgG antibodies is a better marker of the recent infection.