An age-matched group of 247 subjects who had had asthma as children and 39 control subjects were studied with lung function and bronchial reactivity testing at the age of 28 years. Lung function of those who had ceased wheezing was essentially normal, but lung function was increasingly abnormal in those who continued to wheeze. Those with frequent wheezing at 28 demonstrated a greater decline in their respiratory function since the age of 7 years than the other groups. Methacholine provocation testing was performed in 91% of the group and was associated with frequency of wheezing and evidence of small airways obstruction. No association was found between reactivity and loss of ventilatory capacity since 21 years of age.