Forty asthmatic children aged 4 to 6 years performed histamine inhalation tests over 2 to 3 years. We used a previously reported method for examining bronchial hyperreactivity; measuring the transcutaneous oxygen pressure to evaluate whether bronchial hyperreactivity in younger children with bronchial asthma changed, and which potential factors affected changes in bronchial hyperreactivity. Although there was no significant relationship between the severity of asthma and respiratory threshold to histamine (RT-Hist) at the initial test, RT-Hist results in the severely asthmatic group were significantly lower than those of the remission and mild groups at the final test (P less than .01), respectively. RT-Hist significantly decreased in only the group whose asthma worsened (P less than .05). In the remission and improvement groups, RT-Hist did not improve despite their favorable clinical courses. When divided into two subgroups according to the extent of their RT-Hist, a high responder group had significantly more subjects who family histories of asthma than the low-responder group (P less than .05). There was no difference, however, in family history of allergic diseases between the two groups. We conclude that bronchial hyperreactivity in younger asthmatic children is influenced by multiple factors that may be congenital or acquired.