Respiratory function and bronchial reactivity was studied by carbachol challenge in 41 patients with Turner's syndrome and in 46 controls. In patients and controls the personal and family history of atopic illnesses was evaluated; reactivity to skin allergen tests was studied in patients only. Patients with Turner's syndrome had less allergy skin test reactivity; no difference was found in allergic symptoms between patients and controls despite the patients having a more positive family history of atopy (P less than 0.05). Respiratory function variables were higher in patients than in controls, and bronchial reactivity as expressed by the results of carbachol testing was higher in Turner's patients than in controls (P less than 0.01). Bronchial reactivity was significantly reduced after 6 months of estrogenic therapy (P less than 0.05) in subjects with Turner's syndrome, while the same did not occur in patients who did not receive estrogen treatment. This study of pulmonary function and bronchial reactivity in Turner's patients may help understand the effects of sex hormones in the regulation of bronchial tone and of bronchial response to constrictive agents.