Particles having a tap density of less than 0.4 g/cm.sup.3 include a
hydrophobic amino acid or salt thereof and a therapeutic, prophylactic or
diagnostic agent or any combination thereof. Preferred particles include
a phospholipid, have a median geometric diameter between about 5 and
about 30 microns and an aerodynamic diameter between about 1 and about 5
microns. The particles can be formed by spray-drying and are useful for
delivery to the pulmonary system.