The effect of ascorbic acid (AA) on the skin wheal and flare response to histamine and allergen and on the nasal response to allergen was evaluated in eight adults with seasonal allergic rhinitis. The above parameters were measured after 3 days of AA administration (2 gm/day) and again after 3 days of a similar-appearing lactose placebo. An additional study was conducted in which six subjects took 0 (placebo), 1, 2, and 4 gm/day of AA to determine the dose-response effect of AA on histamine skin tests. Overall there was no difference in skin or nasal reactivity between AA and placebo regimens. The findings in this study suggest that AA in relatively high doses would have no beneficial effects on symptoms resulting from allergen exposure and that AA in doses of up to 4 gm/day will not suppress the histamine skin response.