Neem extract containing Azadiractin-A (neem Aza-A), encased in microcapsules, in a matrix of partially hydrolyzed poly(vinyl acetate) crosslinked with glutaralaldehyde 5% (w/v) and 0.05% hydrochloric acid was prepared via a spray drying technique. The photostabilization of unencapsulated and encapsulated neem Aza-A when exposed to ultraviolet light was evaluated. Neem Aza-A solutions and neem Aza-A microcapsules were applied onto the surface of glass slides. At particular intervals, the remaining concentration of neem Aza-A was measured by HPLC. When the ratio of 87% hydrolyzed poly(vinyl acetate) to water was 1:40 this produced the highest concentration of neem Aza-A after exposure to UV. The degree of swelling ratio of microcapsule depended on the crosslinking density and the crystalline content. The neem Aza-A release was measured in water at 25 degrees C and the effects of different matrices and other parameters such as polymer-water ratios and particle size were studied. The release mechanism of the neem Aza-A from the microspheres was also investigated. (C) 2009 Elsevier B.V. All rights reserved.