A new method for measuring nasal resistance is presented by which it is possible to record reproducible and consistent data on nasal flow and resistance. This method was applied to a double blind trial of 2% solution of sodium cromoglycate. Ten adult patients with allergic rhinitis due to grass pollen were assessed during the winter. One nostril was challenged 1 hr after the administration of sodium cromoglycate or placebo given in random order. Eight patients showed significant protection with sodium cromoglycate.