Hypersensitivity to some nematode antigens.

Immediate and delayed skin reactions to antigens derived from Ascaris suum, Necator americanus, and Toxocara canis are described in three subjects and related to eosinophil counts and serum IgE levels. One, who had laboratory contact with ascarides but no known infection, gave positive immediate reactions to all three antigens. Another, following repeated experimental infection with necator, gave positive immediate reactions to all three antigens and a delayed reaction to necator alone. The third, following a single recent infection with necator, gave no immediate or delayed reaction.