The electronic and geometrical properties of endohedrally and substitutionally doped Cd6S6 and Cd12S12 clusters were analyzed by means of Density Functional Theory. The results are compared to those of ZnS clusters of the same size. There is a clear correlation between CdS and ZnS when doped with the same element due to the chemical interaction between the dopant and its host. This is particularly evident from endohedrally doped Cd6S6. The change in properties across the 3d series in doped CdS clusters is not as great as in ZnS clusters.