Pulmonary function was measured in 277 subjects at 21 yr of age who had wheezed before the age of 7 yr, and in a control group that had been followed prospectively for 14 yr. The wheezing group covered the whole spectrum of childhood asthma. Subjects who had minor wheeze in childhood and who had been wheeze-free for at least 3 yr were, as a group, indistinguishable from the control group. There was an increasing incidence of abnormality with increasing frequency of wheezing. Subjects with chronic asthma had a large vital capacity relative to body size at 14 yr of age, but this abnormality was no longer present at 21 yr of age. Bronchial lability to exercise was not a constant finding, and its frequency and severity were related to the frequency of wheezing and baseline pulmonary function. It was estimated that about 60% of the subjects who had ceased wheezing had abnormal bronchial reactivity to inhaled histamine. These subjects should probably not be considered to have "grown out" of asthma.