The purpose of this study was to assess the time of onset of action of acrivastine in suppressing the wheal response to histamine (10 mg/ml) and allergen (10,000 and 100,000 BU/ml) in the skin prick test. Ten subjects with a well-documented allergy to pollen received single doses of 8 mg of acrivastine and placebo according to a randomized, double-blind, placebo-controlled, crossover treatment design. Duplicate skin prick tests were performed 0, 15, 20, 25, 30, and 60 min after medication. The results demonstrated a statistically significant suppression of the wheal reactions 15-20 min after medication, depending on the reaction producers used. The sum of all three producers showed a statistically significant effect on the wheal reaction 15 min after medication. The upper 95% confidence limit for time lag from dosing of acrivastine until reduction from placebo level commences was 6.5 min. The study substantiates that orally administered acrivastine has a rapid onset of action in the skin of allergic subjects. The results indicate that allergen SPT is a more sensitive tool for studying antihistaminergic activity than histamine SPT.