Films of (Zn,Cd)Se and ZnSe were electrodeposited from dimethylsulfoxide solutions of elemental Se and the perchlorates of Zn and Gel. The composition of the mixed selenides could be controlled by variation of the deposition current density, utilizing diffusion control of the low concentrations of Cd(ClO4)(2). The film composition was measured by X-ray photoelectron spectroscopy and compared with the measured bandgap values extracted from optical transmission spectra. Photoelectrochemical photocurrent spectroscopy and contact potential difference (Kelvin probe) measurements both showed changes in apparent conductivity type with Zn concentration in the electrolyte from "n-type" (low Zn) concentration to "p-type" thigh Zn). This phenomenon is discussed in terms of preferential surface trapping of either electrons or holes at the nanocrystallite surface.