Probicromil is a Histamine H1 antagonist. It was taken to the clinic and found to be effective in exercise and antigen challenge. Probicromil inhibited Ascaris-induced bronchoconstriction and the increase in plasma histamine levels seen after Ascaris inhalation. Therapeutic efficacy in seasonal rhinitis was also demonstrated. Further clinical studies were halted because of a side-effect associated with the compound, namely a sensation of warmth (especially in the perineal region) experienced by some volunteers after inhalation.