Twenty-seven patients with hay fever had a carbachol inhalation challenge both out of season and during the pollen season. Eight patients with allergic asthma were used as a control group. Only three patients (11.1%) demonstrated a value of a provocative dose causing a 20% fall in FEV1 in the asthmatic range out of pollen season, but during pollen exposure, the number of positive responses significantly increased to 13 (48.1%). We observed differences regarding mean age, age of onset of symptoms, sex, and family history between patients with positive responses and patients who failed to react to inhalation challenge. It appears reasonable that an aspecific bronchial provocation test, performed during the pollen season, can detect with greater sensitivity patients with hay fever at risk of developing asthma in the future, and it also appears reasonable that these patients should be treated differently from subjects with "pure" allergic rhinitis. We expect the ongoing follow-up to clarify the prognostic value to be attributed to these findings.