The kinetic behavior for coagulation Of ultrafine CdS particles in reverse micellar and homogeneous aqueous solutions was studied with the aim Of understanding the effect of compartmentalization of the particles in reverse micelles on the kinetic behavior. Rapid Coagulation Of CdS particles in aqueous Solution is controlled by the addition of water-soluble thiol-terminated ligands, which are adsorbed on the surface of the particles. The presence of the thiols was found to reduce the rate for coagulation of CdS particles in the reverse micelles as welt as in the aqueous solutions, The rate for coagulation was analyzed on the basis of the pseudo-continuous phase model, in which the water cores in the reverse micelles, were assumed to act as a continuous phase via the rapid exchange of the contents Of the cores. The rate constants for both systems were found to he almost identical, except in the case of the reverse micellar systems of a low water content, where the reverse micelles are as small as the particles.