Small particles of two steroids; cholesteryl acetate and b-sitosterol, have been prepared by the following technique: The steroid was dissolved in an organic solvent, which was emulsified in water in the presence of sur--factant, thus giving a water continuous emulsion. As the organic solvent was evaporated the steroid precipitated. One particle was found to form in each emulsion droplet. Particle sizes down to 25 nm were obtained by this method. Particles were prepared from emulsions containing different organic solvents and surfactants and the effect on the size and the colloi--dal stability of the particles were examined. It was found that the final particle suspension is relatively stable provided the initial emulsion is stable. Furthermore, there is a close correlation between the initial emul--sion droplet size and the final particle size. The particle size, therefore, can be varied in the same manner as the size of emulsion droplets, e.g. by changing the emulsification process parameters, the amount and choice of surfactant and the oil/water ratio. Finally, the particle size depends on the choice of solvent and only slightly on the concentration of drug in the oil phase of the emulsion.