Urinary N tau-methylhistamine during early and late allergen-induced bronchial-obstructive reactions.

Urinary N tau-methylhistamine, a unique histamine metabolite, was determined in 29 patients with bronchial asthma before and after inhalation of a control solution on 1 day and before and after allergen inhalation on another day. Twenty-eight patients had an early bronchial-obstructive reaction, defined by a decrease in FEV1 of 20% or more within 1 hr after allergen inhalation. A late bronchial-obstructive reaction, 3 to 8 hr after allergen inhalation, was found in 16 patients.