A single blind, cross-over study was performed in 12 male, nonsmoker, stable asthmatics, to assess the bronchodilatory responsiveness attributable to sympathetic and parasympathetic mechanisms. Serial doses of one agent (salbutamol or ipratropium) were administered to the supramaximal level to produce the maximum achievable bronchodilatation; thereafter, the other drug was given. The sequence was reversed on the 2nd day. On the 3rd day, both drugs were given together from the very beginning. Significant initial bronchodilatation was observed with either agent given alone, but was more marked with salbutamol. Further additional bronchodilatation was seen when salbutamol was administered after ipratropium, but not with ipratropium given after salbutamol. It was concluded that all achievable bronchodilatation was obtained with the adrenergic agent (salbutamol) given alone and that the dominant autonomic control of bronchomotor tone in bronchial asthma is through adrenoceptors.