In the course of the follow-up of 206 previously obstructive bronchitis children, the effect of parental smoking upon the occurrence of respiratory diseases, the yearly frequency of wheezing episodes and the age until the obstructive episodes used to return have been investigated. Familial and maternal smoking was more frequent in this group compared to the control group. In spite of this, however, no correlation could be detected between familial smoking and frequency of respiratory diseases, as well as the above mentioned characteristics of obstructive bronchitis. The familial smoking did not seem to influence the bronchial hyperreactivity challenged with acetylcholine, although the prevalence was higher.