We studied the change from childhood to adulthood in skin test reactivity to house dust, animal dander, grass pollen, and molds, and, in addition, the change in number of blood eosinophils. The study was carried out in a group of 119 children with asthma, aged 6 to 14 years first observed between 1966 and 1969. In the present study, 101 subjects (85%) were reinvestigated after a mean period of 16 years; 43% had current symptoms. Skin test reactivity to all allergens and the number of subjects with positive skin tests to more than one allergen increased from childhood to adulthood. Subjects with allergic rhinitis (38%) had a higher number of positive skin tests to grass pollen in both childhood and adulthood than subjects without allergic rhinitis. Fifty-three children and 10 adults had atopic dermatitis. Atopic dermatitis occurred with equal frequency in children who did and in children who did not have current symptoms later in life. No differences in skin test reactivity to allergens were found between smoking and nonsmoking subjects. Although the smoking period was relatively short, smoking was correlated with eosinophilia in adulthood. The mean number of eosinophils decreased significantly between the first and second survey. The outcome of childhood asthma as defined by current symptoms was not predicted by skin reactivity to allergens, eosinophilia, atopic dermatitis, or allergic rhinitis in childhood.