In 12 asthmatic patients with mild airway obstruction we have measured the effect on specific airway resistance (sRaw) of inhaling the smoke of one Datura stramonium cigarette. In 11 patients sRaw decreased substantially after the cigarette, the mean maximal decrease being 40% at the 30th minute. In seven patients the subsequent inhalation of 200 micrograms salbutamol caused no further decrease in sRaw. In the remaining four patients salbutamol induced a larger decrease in sRaw than the cigarette smoke. The inhalation, however, of a synthetic anticholinergic agent (SCH 1000, 600 micrograms) proved as effective as salbutamol in these patients. In one patient the cigarette smoke and SCH 1000 produced only a negligible amount of bronchodilatation whereas the bronchial obstruction was reversible with salbutamol. Minor side effects were observed in six patients after the cigarette.