The inhibitory effect of orally administered dexchlorfeniramine (4 mg/day), cyproheptadine (8 mg/day), astemizole (20 mg/day), loratadine (40 mg/day) and terfenadine (120 mg/day) on the size of histamine-induced weals was tested by skin prick test with histamine in an open study including 23 healthy individuals. The antihistamines were administered for 2 days in the nationally recommended therapeutic doses. For all drugs the maximal weal suppression with the dosage chosen was recorded the day after the last dosage, being 29% (for dexchlorfeniramine), 72% (for cyproheptadine), 50% (for astemizole), 62% (for loratadine), and 56% (for terfenadine) of the baseline value. For the drugs in the same order the duration of the inhibitory effect of the drugs after the last dose administered was between 3-4, 7-11, 17-28, 4-7, and 4-7 days, respectively.