The photoconductivity in cadmium selenide single crystals is investigated to determine if the Klasens picture properly describes the electronic phenomena in this material. It is found that the simple two-state model is inadequate and at least three recombination centers, and possibly four, are needed for consistency. It is furthermore found that for the model to be acceptable, it must be assumed that activation occurs at impurity levels below that available in the purest material. Some of the limitations of using sintered photoconductors in a study of this type are also described. © 1963 The American Institute of Physics.