Forty-eight wheezy infants were followed up for 25 to 44 months. These infants were classified into three groups: those with asthma (developed asthma later), the wheezy group (had successive wheezing episodes), and the non-wheezy group (grew out of the wheezy episodes). Serum IgE levels at the first visit were not significantly different in the three groups, but the frequency of exposure to cigarette smoke was higher in the asthma and wheezy groups than in the nonwheezy group.