BACKGROUND: Medications can modulate the results of skin prick tests (SPTs). Short-term corticosteroid therapy does not alter IgE-mediated skin tests, but the impact of long-term oral corticosteroid therapy on SPT results is unclear. A prospective study was carried out in patients with steroid-dependent asthma who received oral corticosteroids for a long period to determine whether this treatment reduced skin test reactivity. METHODS: Thirty-three patients with steroid-dependent asthma (median age, 59 years) were compared with 66 patients with asthma who served as a control group, matched for age, sex, and atopic status. SPTs with codeine phosphate and a screening battery of standardized allergen extracts were performed before commencement and after at least 1 year of daily oral prednisone treatment (median duration, 2 years; median daily dose, 20 mg). RESULTS: Fifteen patients with corticosteroid-dependent asthma were allergic before treatment, and their sensitization was not changed by long-term treatment with oral corticosteroids. The median wheal diameters induced by codeine phosphate were similar in both groups. The median wheal diameters induced by allergens, and more specifically, by Dermatophagoides pteronyssinus and D. farinae were similar in both groups and did not change in the steroid group after treatment. CONCLUSIONS: Systemic corticosteroid therapy (prednisone, 10 to 60 mg/day) for 2 or more years does not seem to alter SPT reactivity. (J ALLERGY CLIN IMMUNOL 1996;98:522-7.)