We studied the effect of ascorbic acid in 14 mild asthmatic subjects. The effect of ascorbic acid (1.0 g orally) was assessed by the changes in concentration of methacholine required to decrease the specific airway conductance by 40% (pD40). Ascorbic acid increased pD40 from control values of 9.38 +/- 1.97 mg/ml (mean +/- SEM) to 12.59 mg/ml +/- 2.52 (p less than 0.05). Administration of 50 mg of indomethacin, orally, reversed the effect of ascorbic acid. Indomethacin alone had no effect on the mean pD40. The results suggest that ascorbic acid exerts its effect via alteration of arachidonic acid metabolism.