Epidemiological studies report a 50% incidence of at least one wheezing episode in young children. If we can argue that 10% of children have asthma sometime during their pediatric years, it still leaves a significant percentage of children with an unexplained cause for their wheezing. Other recognized phenotypes of recurrent wheezing include young children exposed to excessive environmental tobacco smoke (ETS), while other infants wheeze recurrently following a significant episode of bronchiolitis. Bronchial hyperresponsiveness (BHR) is a universally recognized phenomenon of asthma, but its presence in young children with recurrent wheezing is not as well studied. Currently available studies demonstrates that BHR is also seen in young pediatric asthmatics, paralleling what is well recognized in adolescent or adult asthma. In those children with post-bronchiolitis wheezing, BHR appears to be present to a degree; while infants and young children exposed to ETS have increased BHR, as a group. If exaggerated BHR in recurrent wheezing children without asthma has the same inherent disadvantage as it does in asthmatic children, additional studies looking directly at this issue in a longitudinal fashion need to be designed. A hypothesis of BHR in non-asthmatic children is presented that could be studied prospectively.