HA-coatings have been widely used in human surgery to increase the biocompatibility of metal alloys used as arthroplasty material. Their characteristics are of fundamental importance for their behaviour in the organism and in particular their degradation rate. We had the opportunity to perform histological analysis of human femurs containing well functioning HA-coated hip prostheses implanted for various periods from a few days up to several years. It was showed that the coatings exhibit degradation signs very early after the implantation and the released debris have different fates depending their size and shape. These results can be compared with those obtained in animals or in vitro. It was shown that the bone tolerate the contaminant phases which can be formed during the plasma spraying.