The effect of drinking 40 ml of sherry on peak expiratory flow rate in 16 normal subjects and 19 patients with asthma was assessed after oral administration of either chlorpropamide or placebo. After placebo and sherry normal subjects showed no change in peak expiratory flow rate, while an increase was usually shown by patients with asthma. This bronchodilation was more marked in patients whose base-line peak flow rate was less than 50% predicted. Ingestion of chlorpropamide before sherry significantly modified the bronchodilating properties of sherry; five of the 19 patients with asthma showed airway narrowing on 11 of 19 occasions tested. Further studies in one patient suggest that this bronchoconstriction may be mediated by congeners in sherry rather than ethanol. These findings confirm the observation that chlorpropamide and sherry can cause airway narrowing in patients with asthma but shows that this response is not always reproducible. The bronchodilator effect of alcohol in patients with asthma may have therapeutic implications.