Maternal narcotic abuse and neonatal thrombocytosis.

responsiveness as severe as that of the asthmatics. Moreover, with very few positive airway responders in a small study group it would be difficult to show a significant difference statistically, even if such a difference had existed. Additionally, without a reference population, they cannot say whether their findings were normal or abnormal. In our own study of a cohort of low birthweight children we found that the distribution of a positive airway response to histamine formed a continuum.3 At very low doses of histamine very few subjects in either the low birthweight cohort or a reference group showed a positive airway response. On the other hand, a significantly greater proportion of low birthweight children had a positive airway response, at moderate histamine doses, suggesting a shift in the frequency distribution of airway responsiveness. Children with bronchopulmonary dysplasia were slightly more responsive than other low birthweight children. We agree with the findings of Duiverman and colleagues that very few children with bronchopulmonary dysplasia have a degree of airway responsiveness to histamine similar to recognised asthmatic subjects. Many do, however, show a mild to moderate increase in airway responsiveness when compared with an appropriate reference population. We are therefore unable to agree with their conclusion that 'bronchial responsiveness to histamine in these subjects (bronchopulmonary dysplasia survivors) was normal'.