Sixty-seven atopy-prone children (atopic family group, AFG) and 52 children with no family history of atopy (NAFG) were followed for 10 years. During infancy, the mothers of the newborn AFG children were advised to adjust their infants' diet, with a view toward minimizing the risk of atopy, and not to keep pets. Pulmonary function tests, methacholine inhalation challenge (MIC), and skin prick tests (SPT) were done in order to evaluate the bronchial reactivity and skin reactivity in the two groups. A pathological result in MIC was found in 20 (30%) of the AFG children and in 10 (19%) of the NAFG children. Such results of MIC were more common in the children with positive SPT results than in those without (67% vs. 24%). In regard to the diet consumed in infancy, MIC was pathological in 23% of children with and in 36% without prophylactic diet in infancy. For MIC, using the new, Spira electro 2 dosimeter equipment, the sensitivity was 75% and specificity 97%, but the predictive value for diagnosing bronchial asthma was only 25%. The important advantage of our method is that the degree of bronchial reactivity can be estimated by responses to increasing provocative doses. Our observations confirm that the new method is suitable for detecting bronchial asthma in clinical practice but it seems not to be optimal for epidemiological studies. We concluded that later bronchial hyperreactivity can not be diminished by avoiding home pets or providing a hypoallergenic diet during infancy.