Thirty patients with chronic obstructive pulmonary disease had their vital capacity (VC) and forced expiratory volume in one second (FEV1) measured before, one-half hour after, and two and a half hours after they breathed aerosols of isoproterenol (cartridge M), isoproterenol with phenylephrine (cartridge D), or a placebo. The placebo had negligible mean effects. Thirty minutes after each isoproterenol cartridge there was a rise in mean VC and FEV1 which was statistically significant compared to the change 30 minutes after the placebo. There was no significant difference between the two aerosols in effect on VC or FEV1 at 30 minutes. Two and one-half hours after the inhalations, there was no significantly greater persistent effect on VC or FEV1 after cartridge D than after cartridge M. Cartridge M had greater effects on VC than D when used initially; when used as a second dose its effects were halved, possibly because in the study it was given after tolerance to isoproterenol had developed after the administration of cartridge D.