To eliminate reactivity against antigenic determinants shared by the ascarid worms A. lumbricoides and Toxocara spp., human sera were absorbed with somatic antigen of A. lumbricoides before measurement of anti-Toxocara IgG. The A. lumbricoides somatic antigen was prepared as described previously [15]. Because 10.7% of the children were infected with T. trichiura, some samples of the studied sera were also absorbed with this parasite extract and compared to the same sera absorbed with A. lumbricoides alone or with both parasites, but because absorption with A. lumbricoides alone or with both parasites provided comparable titers of anti-Toxocara IgG, the remaining sera were absorbed with A. lumbricoides antigen alone.