Sixteen White children with bronchial asthma were divided into two groups; one received standard anti-asthma chemoprophylaxis (SAC) and the other SAC supplemented with 1 g ascorbic acid (Redoxon) given as a single daily dose for a 6-month period. In 10 patients the effects of ascorbic acid on exercise-induced bronchoconstriction (EIB) were assessed by comparing the pre-ascorbic acid results with those obtained 2 1/2 hours after the intravenous injection of 1 g ascorbic acid. Immunological investigations performed on the two groups were assessment of polymorphonuclear leucocyte (PMNL) motility, phagocytosis and nitroblue tetrazolium reduction and measurement of secretory IgA, serum immunoglobulin and total haemolytic complement levels and levels of the components C3 and C4, alpha 1-antitrypsin, antistreptolysin O (ASO), C-reactive protein and antibodies to certain respiratory viruses. These investigations were performed before and 1, 3 and 6 months after the commencement of therapy. Radio-allergosorbent testing for sensitivity to four common allergens was carried out at the outset and after 6 months of therapy. Injection of ascorbic acid had no detectable effects on the degree of EIB. Slight but not significant immunological changes were observed in the SAC group over the 6-month study period. However, in the SAC plus ascorbic acid group significantly improved PMNL motility and decreased ASO levels and reduced (although not to a significant extent) IgE levels and titres of antibodies to the respiratory viruses were observed.