Lomustine and progesterone have been incorporated in biodegradable poly(d,l-lactide) microspheres by evaporating dichloromethane from stirred dichloromethane-in-water emulsions. Spherical microspheres with lomustine or progesterone payloads less than or equal to 23% were obtained. Higher lomustine payloads gave irregularly shaped particles. Microspheres with less than or equal to 68% progesterone were obtained, but free drug crystals formed on the surface of such microspheres. Increased agitation rates decreased mean microsphere size. Addition of drug to the dichloromethane phase increased average particle size relative to that obtained with drug-free microspheres prepared under the same experimental conditions. Complete evaporation of the dichloromethane, while the medium was continuously stirred, promoted formation of free drug crystals in the aqueous phase. Increased emulsifier concentrations did not significantly enhance drug incorporation efficiency within the microspheres. Shelf-life stability of lomustine and progesterone was reduced by incorporation in the microspheres, presumably due to their molecular dispersion in the poly(d,l-lactide).