Clinical course and sequential IgE values were recorded in a 4-year prospective study of 80 atopic wheezing babies at ages from 6 months to 4-5 years. At final assessment, 68% of the children had been symptom-free for at least 1 year whilst 32% still suffered from wheezing attacks. Total IgE levels from the first visit until final assessment were greater than 2 SD above normal for age in 63% of all children, but no significant correlation could be found between sequential IgE levels and the clinical picture or course of the disease. In all cases IgE levels rose steadily with increasing age, independently of whether wheezing disappeared or persisted. The most significant rise in IgE values occurred between 1 and 2 years of age, and IgE levels at 4 years could be predicted by the value at the age of 2 years (r = 0.97). In the group of children that lost their wheezing tendency there was: a significantly greater number of infants that were breast-fed during at least the first 3 months of life (P less than 0.01), a lower incidence of exposure to parental smoking (P less than 0.01), and a lesser incidence of lower respiratory tract infections (P less than 0.01). Though there was no correlation between increase of IgE levels and type of feeding or exposure to cigarette smoke, statistical data confirms that bottle feeding and parental smoking lead to persistence of wheezing in atopic children.