A novel formulation technique to manufacture large hollow carrier particles of nanoparticulate drugs for inhaled drug delivery is developed in the present work. The large hollow carrier particles, whose shells are composed of nanoparticles aggregates, are manufactured via the spray drying of nanoparticulate suspensions under a predetermined operating condition. The large and hollow features of the carrier particles (d(g) approximate to 10 mu m; rho(e) << 1 g/cm(3)) are purposely formulated to produce carrier particles that have high flowability and high therapeutic efficacy, which are crucial for a successful drug delivery to the lungs. Polyacrylate and silica nanoparticles of various sizes (5-150 nm), without loaded drugs, are used as the model nanoparticles. The focus of the present work is to investigate the effects of size, chemical nature, and feed concentration of the nanoparticles on the morphology and degree of hollowness of the spray-dried carrier particles. The chemical nature of the nanoparticles, not the size, is observed to be the determining factor in the hollow particle formation, as evident in the varying results of the effects of changing the concentration among nanoparticles of different chemical nature.