The outcome of childhood asthma was studied in 101 adults who came from a group of 119 asthmatic children (85%) 6 to 14 yr of age who had originally been investigated between 1966 and 1969. Changes in respiratory symptoms, spirometry, and airway responsiveness to histamine in childhood and adult life were analyzed. It was found that 43 of the 101 adults (43%) had current symptoms; 29 of the 43 (67%) were receiving maintenance therapy. In the first study, 83 of the 101 children (82%) showed a response on inhalation of histamine (PC10-histamine less than or equal to 16 mg/ml). The number of subjects in the second study who still had a PC10-histamine less than or equal to 16 mg/ml fell to 29, suggesting that airway responsiveness decreases from childhood to adulthood. During the second survey (in adults), 25 of the 43 (59%) subjects with current symptoms and four of the 58 (7%) without respiratory symptoms responded to histamine. Adults with current symptoms had a significantly lower %FEV1 in both childhood and adulthood than did adults without current symptoms; %FEV1 was not different in females and males or in smokers and nonsmokers in either the first or the second survey. The outcome of childhood asthma is primarily predicted by the initial degree of bronchial obstruction (p = 0.041) and airway responsiveness to histamine (p = 0.050), and does not appear to be related to sex, smoking habits, or age of onset of respiratory symptoms.