Crystal data for CuInSe₂

X-ray data is presented and analysed for the semiconducting compound CuInSe₂, prepared by zone levelling. Values of a = 5.782 and c = 11.620 Å, have been determined and intensity calculations have been used in the evaluation of interatomic separation and bond angles. Some aspects of stoichiometry, related to electrical characteristics, are discussed and it seems probable that the structure of the compound is modified by a small concentration of Se vacancies.