The efficacy and side effects of two approaches to the treatment of ragweed pollen-induced rhinoconjunctivitis were compared in a double-blind, parallel-group trial. Sixty ragweed-sensitive adults were randomized either to a course of four Pollinex-R hyposensitization injections during the 6 weeks before the ragweed-pollen season, or to budesonide aqueous nasal steroid spray, 400 micrograms daily, throughout the season. A double-dummy technique was used to achieve blinding. During the ragweed-pollen season, troublesome nasal symptoms were treated with terfenadine, 60 mg, when treatment was needed, up to 240 mg daily, and eye symptoms were treated with naphazoline eye drops, when treatment was needed, up to four times daily. Every day, subjects recorded the severity of nasal and eye symptoms and medication use in a diary. Fourteen of the subjects receiving Pollinex-R were unable to complete the course of injections because of systemic or large local reactions. Eight subjects withdrew during the pollen season because of severe rhinitis; all subjects had received Pollinex-R. Subjects in the budesonide-treated group had minimal nasal symptoms and used very little terfenadine, compared with subjects in the Pollinex-R-treated group (p less than 0.0001). Eye symptoms and eye drop use were similar in the two treatment groups. No clinically important side effects were reported by the subjects receiving budesonide. The results of this study suggest that aqueous budesonide nasal spray is markedly more effective than Pollinex-R in controlling symptoms of seasonal rhinitis while the side effects and inconvenience of immunotherapy are avoided.