In order to maintain a colony of rhesus monkeys with IgE-mediated Ascaris asthma, we evaluated the response of four animals to infection with Ascaris suum ova. All four animals developed immediate-type cutaneous reactivity and airway responses. Serum IgE and IgG antibody responses against Ascaris antigen, as quantitated by the ELISA, were seen in all animals. Peripheral blood histamine release after stimulation with Ascaris antigen was positive in all animals. Airway reactivity to aerosol challenge with Ascaris antigen became positive in all animals and has remained positive for 6 months in three of four animals. Both standard and threshold dose airway types of responses were present. Except for transient eosinophilia, the animals remained in good health. The studies demonstrate that infection with A. suum results in rhesus monkeys with IgE-mediated immediate-type reactivity that simulates the naturally occurring model of asthma.