Morphology dependent resonances (MDR) are observed in the fluorescence spectra of 9-amino acridine hydrochloride hydrate (9AAHH) in polymer spherical microparticles. Decrease in the fluorescence lifetime as a function of the size of the microparticle indicates the enhancement of the radiative rate. The results have been explained on the basis of cavity quantum electrodynamic (QED) effects. It is shown here that the appearance of MDR and the enhancement of the radiative rate are controlled by the size and the shape of the microparticle. (C) 2003 Elsevier Science B.V. All rights reserved.