1. The excretion of 1-methylimidazole-4-acetic acid (MeIAA) in urine was measured in three groups of asthmatic children (acute-symptoms, quiescent and steroid-treated) and a control group of hospitalized non-asthmatic children all on the same restricted diet. 2. There was no statistical difference between the excretion of MeIAA in urine in any of the groups. There was therefore no evidence of impairment of the methylation pathway of histamine metabolism in asthma.