A method and device are provided to generate an aerosol having a desired particle sizes, i.e., from molecular to about 10 microns, which can be used to effectively deliver a physiologically active compound to organs and tissues such as the lung, eye, mucosa and skin. The aerosol is formed through vaporization of the compound while mixing the resulting vapor with a gas, in a ratio, to form the desired particle size when a stable concentration of particles in the gas is reached.