The invention generally relates to a method for pulmonary delivery of therapeutic, prophylactic and diagnostic agents to a patient wherein the agent is released in a sustained fashion, and to particles suitable for use in the method. In particular, the invention relates to a method for the pulmonary delivery of a therapeutic, prophylactic or diagnostic agent comprising administering to the respiratory tract of a patient in need of treatment, prophylaxis or diagnosis an effective amount of particles comprising a polycationic complexing agent which is complexed with a therapeutic, prophylactic or diagnostic agent or any combination thereof having a charge capable of complexing with the polycationic complexing agent upon association with the bioactive agent. The particles can further comprise a pharmaceutically acceptable carrier. The amount of polycationic complexing agent present in the particles is an amount sufficient to sustain the release of diagnostic, therapeutic or prophylactic agent from the particles. For example, the amount of complexing agent present can be at about 5% weight/weight (w/w) or more of the total weight of the complexing agent and therapeutic, diagnostic or prophylactic agent. Release of the agent from the administered particles occurs in a sustained fashion.