Hydroxyapatite and other related bioactive materials are ceramics which are not only biologically compatible but have the ability to integrate with new bone growth. They are already being marketed as coatings for hip implants and other endoprostheses, with the expectation of improved bonding to the natural bone. To date, however, none of the coated implants available have demonstrated any significant improvement over conventional implants. Most previous research has concentrated on the biological activity of the coating, and although it has included microstructural characterisation, the influence of residual stresses which can play a key role in material failure, have been neglected. In this paper, we present the first results of a study relating the residual stress in plasma sprayed KA coatings, determined using X-ray diffraction, to the deposition parameters, microstructure and phases present in the coating.