Allergic rhinitis is a particularly good model for studies of cytokine production in vivo. In this study the occurrence of the cytokines IL-4, IL-5, IL-10 and IFN-gamma as well as the soluble receptor for IL-4 in nasal lavage fluids were assayed in 38 school children, with seasonal allergic rhinitis, and 19 healthy age-matched, non-atopic controls, using highly sensitive enzyme immunoassays. IL-4 levels in patients with seasonal allergic rhinitis were markedly increased in comparison with those in non-atopic controls or in atopic patients before the start of the pollen season. In controls, but not in the atopic patients, levels of IFN-gamma and IL-5 were significantly higher in specimens obtained during the pollen season than in those obtained outside the season. The IL-4/IFN-gamma ratios were significantly higher in atopic than in non-atopic subjects and further increased in atopic patients during the season. In addition to IL-4, elevated levels of IL-10 were observed in association with seasonal rhinitis. Following treatment with a topical steroid (budesonide) there was a statistically significant increase of the levels of soluble IL-4 receptor. These findings indicate that nonatopic and atopic individuals react to pollen exposure with distinct cytokine patterns in agreement with the Th1/Th2 concept. Topical steroids may possibly decrease inflammation by increasing the formation of soluble IL-4 receptor.