Cadmium sulfide (CdS) thin films pure and doped with indium (CdS : In) were obtained by chemical spray. Growth rate, crystalline structure and optical properties are reported. Polycrystalline structure with preferred (0 0 2) orientation was obtained. For CdS : In thin films, the lowest resistivity value obtained was around 3 x 10(-2) Ohm cm. The absorption edge remains practically constant, as the substrate temperature is increased and the impurity concentration in the solution [In]/[Cd] is less than 0.1% atomic. For higher atomic ratios in the solution, such as 8%, the band gap tends to decrease with the substrate temperature.