Bronchodilatation was produced in normal subjects by the inhalation of a parasympatholytic agent (atropine) and the response was compared to that occurring after the inhalation of a beta-adrenergic agent (isoetharine). Doses were chosen that resulted in equivalent increases in specific airway conductance (78 +/- 9% for atropine; 88 +/- 21% for isoetharine). Anatomic dead space and volume at the onset of the terminal nitrogen rise (closing volume) were measured before and after each agent. Although there was no difference in the degree of overall bronchodilatation after the two drugs, anatomical dead space increased significantly more after atropine than isoetharine (+17% vs. +6%, P less than 0.01), and closing volume increased significantly after isoetharine (P less than 0.005) but did not change with atropine. We interpret these differences to indicate a greater effect of cholinergic antagonists on the more central airways and a greater effect of beta-adrenergic stimulants on peripheral airways.