Inhaled bisulfite (HSO3) aerosol produces bronchoconstriction in asthmatics but not in normals. This effect is probably due to local formation of SO2 which stimulates vagal afferents in the airway mucosa, and gives rise to bronchoconstriction that is partly due to a cholinergic reflex. Metabisulfite (MBS) produces bronchoconstriction in most adult asthmatics, but its effect in children has received little attention. The present study was done to assess MBS-induced bronchoconstriction as a function of age in asthmatic children, and to compare MBS responsiveness with the response to inhaled metacholine (MCH), which is commonly used for bronchoprovocation testing. In 36 children with moderate asthma, selected to cover the age range between 3 and 20 years, we compared airway responsiveness to MBS and MCH, expressed as the provocative dose that causes a 20% fall in baseline forced expiratory volume in 1 sec (FEV1, PD20). We also measured the PD20 to MBS after pretreatment with the anticholinergic ipratropiumbromide, to estimate the noncholinergic component of the response. After bronchial provocation with MCH, a PD20 was reached in 32 children, and no significant relation of PD20 to age was found. A PD20[MBS] was seen in only 17 patients, and more frequently in older children. There was a significant negative correlation between age and PD20[MBS]. Ipratropium pretreatment reduced the response to MBS in 14 of the 17 children who had a PD20[MBS]. The PD20[MBS] after ipratropium pretreatment was also significantly negatively related with age. This suggested that the increased prevalence of MBS responsiveness was due to an increase of the noncholinergic component of the response.(ABSTRACT TRUNCATED AT 250 WORDS)