The solubility of Ag in CdS has been measured under conditions of excess sulfur between 375° and 900°C. Also, the distribution coefficient of Ag between CdS and liquid Cd for dilute Ag concentrations has been measured between 500° and 900°C. In addition, the distribution coefficient has been measured at 800°C as a function of the composition of the Cd‐Ag alloy. These solubility measurements are interpreted to indicate at least two and probably three different forms of Ag in CdS. Diffusion profiles have been obtained between 300° and 500°C. The rate of diffusion of Ag shows a strong concentration dependence and is extremely rapid for dilute Ag concentrations. The profiles are discussed in terms of three independent steps in the incorporation of Ag in CdS.