Betamethasone valerate nasal aerosol in a daily dose of 400 micrograms was compared with a placebo in a double-blind trial involving 103 patients with summer hay fever. The patients' and physicians' preference for the active compound was statistically significant (P less than 0.001), with 88% of the patients receiving betamethasone valerate obtaining substantial relief of symptoms. The analysis of patients' daily symptom scores showed that nasal symptoms were significantly reduced by the active aerosol (P less than 0.001). A day-by-day comparison of nasal symptom scores with pollen counts indicated a decreasing allergic response as the season progressed; possible reasons for this are discussed. No clinically significant side effects were observed. Short tetracosactrin tests from ten randomly chosen patients on betamethasone valerate showed no abnormality and nasal swabs for Candida culture from a further thirty-two patients were negative. It is concluded that intranasal betamethasone valerate is an effective and safe form of therapy for seasonal rhinitis.