Ninety-two children, sixty-two boys and thirty girls, aged 18 months to 6 years with frequent asthma were studied. Nine were born prematurely and two were ventilated in the neonatal period; two had been admitted to hospital with acute bronchiolitis. Most had an early onset of symptoms, forty-two developing asthma in infancy. Although overall growth was normal, 63% had some chest deformity. Half had past or present eczema and just over half had chronic rhinitis. Upper respiratory infection appeared to be an important precipitant of attacks in all, and 88% had exercise-induced asthma. The majority were atopic, 74% had elevated serum IgE levels, skin-prick tests were positive in 61 of 77 tested and half had eosinophilia. However, allergic factors were clearly identified as causing asthma attacks in only 24%. Immunoglobulin deficiencies were found in thirteen and defective yeast opsonization in eighteen; these children showed no other obvious differences from the remainder. Eighty-two children were followed up and after 1 year fifty-one were receiving inhaled steroids. Measurement of serum immunoglobulin, eosinophil count and skin-prick testing had little influence on management.