Early recognition of infantile asthma in wheezing infants is a major problem for physicians. We investigated whether detection of early sensitization to inhalant allergens would be useful to identify those wheezing infants who are likely to develop asthma. A total of 67 infants (aged 1-25 months) hospitalized for a wheezing episode were initially tested for reactivity to inhalant allergens by both skin prick test and in vitro measurement of specific IgE antibodies (Phadiatop). Thirty-seven of the infants were already considered to have infantile asthma, and 30 presented only their first or second wheezing episode when included in the study. All infants were followed for a mean period of 18 months. Seventeen (25%) infants, including seven infants initially not asthmatic, had positive prick test to Dermatophagoides pteronyssinus or to cat fur. All of these children were diagnosed as suffering from infantile asthma at the end of the follow-up. Thus, skin test positivity to inhalant allergens was significantly associated with the diagnosis of infantile asthma (P < 0.05) and could be considered to be predictive of the development of infantile asthma (P < 0.03). In contrast, Phadiatop was less sensitive than skin prick tests, and only five children had positive in vitro test results, suggesting that specific IgE may primarily bind to tissue mast cells before being detectable in serum. We concluded that sensitization to inhalant allergens may distinguish wheezing infants who develop asthma from those who do not, and that skin testing may assist the early diagnosis of asthma in wheezing infants.