Children suffering from seasonal allergic rhinitis (SAR) and matched normals were instructed on the use of a didactic computer simulation. Groups of SAR children received different treatments before instruction; i.e., sedating or nonsedating antihistamines or placebo. All returned after 2 weeks for an examination measuring factual and conceptual knowledge and the application of a learned strategy. Examination results showed large impairing effects of SAR on prior learning. That effect was modified by the drug treatment relative to placebo. Conclusion: SAR and sedating antihistamines combine to reduce children's learning ability.