Uniform CdS particles with an average diameter of 40-100 nn were prepared in large quantities by aging for 1 h at 20 degrees C 1.0 mol dm(-3) Cd(OH)(2) suspensions containing 1.1 mol dm(-3) thioacetamide (TAA), 1.0 mol dm(-3) NH4NO3, and 1 wt% deionized gelatin in the presence of ammonia of various concentrations. No uniform CdS particles were formed when gelatin was not added to the system or when pH was adjusted with NaOH instead of NH3. The CdS particles grew via solution phase by a reaction of ammonia complexes of Cd2+ supplied by the dissolution of Cd(OH)(2) and S2- released from TAA.