A manual-injection liquid chromatographic method using fluorescence detection permitted determination of a new antiasthmatic drug, azelastine, and its desmethyl metabolite extracted from human plasma. Reliable quantitation was achieved to at least 0.3 ng/ml for each analyte. No interference was seen in co-chromatography of sixteen other substances, which were potential co-medications (or their metabolites) as used in standard asthma or allergy treatment.