Proliferative responses and production of IL-2 by peripheral blood mononuclear cells of patients with Dermatophagoitles pieronyssinus rhinitis ± asthma were measured at up to 24 hr intervals from 1–8 days, after stimulation with mitogen (PHA), antigen (SKSD) and specific allergen (D.pteronysxinus). IL-2 was measured in culture supcrnaunts using the murine CTLL cell line bioassay. Compared to non-atopic controls, patients had significantly higher prolilenitive responses to D. pteronyssinus and SKSD but similar responses to PHA. In patients, maximal proliferate responses to PHA, SKSD and D. piemnyxsinus were at 3, 6 and 7 days, respectively. IL-2 levels in response to stimulation with D. pieronvssinus were significantly higher in patients than controls, where only background levels were found (15.4, 7.9–30.7− 10-2 U/ml [mean, range] n=11;vs 2.2,0.1–8.4 × 10-2 U/ml, n= 6; P< 0.05). In contrast, IL-2 production to PHA and SKSD, although higher in patients, was not significantly different than controls. These results suggest allergic patients possess a population of T cells expandable by specific allergen which are induced to secrete IL-2.