A method for delivering an agent to the pulmonary system, in a single, breath-activated step or a single breath, comprises administering from a receptacle enclosing a mass of particles, to a subject's respiratory tract, particles which have a tap density of less than 0.4 g/cm.sup.3 and deliver at least about 50% of the mass of particles. The particles are capable of carrying agents. The agent is (1) part of the spray-drying pre-mixture and thereby incorporated into the particles, (2) added to separately-prepared particles so that the agent is in chemical association with the particles or (3) blended so that the agent is mixed with, and co-delivered with the particles. Respirable compositions comprising carrier particles having a tap density of less than 0.4 g/cm.sup.3 and a composition comprising an agent are also disclosed. Methods of delivering these respirable compositions are also included.