In this study, the morphology of the Hydroxyapatite (HA) coatings sprayed on Ti alloy samples by Detonation Gun Spray (D-Gun) and the effect of aging before and after heat treatment in physiological solution were observed. Cross-sectional porosity and percentages of amorphous and crystal phase were measured using optical, electron microscopy, and X-ray diffraction analysis. Differential Thermogravimetric Analysis (DTA) was performed to estimate the glass-crystalline phase transformation temperatures. Heat-treatment at 300, 500, 700, 800 and 1200 degrees C were carried out to confirm DTA results. As a final analysis, the aging effect using Ringer's solution for 1 week on heat-treated and non-heat-treated samples was measured, It was observed that, in D-Gun sprayed samples, the cross-sectional porosity stayed in the accepted 5% range as reported for other spraying techniques,(1-5) On the other hand, surface porosity measured using the water immersion method remained in the conventional porosity limit of 15% for non-heat-treated samples. Heat-treatment had a small influence on the porosity while the crystallinity increased considerably; in addition, aging had little effect on HA crystallinity for heat treated samples. This work showed that D-gun sprayed HA coatings had lower porosity and better integrity than other coatings, due to which we can expect better performance during in vivo applications. (C) 1999 John Wiley & Sons, Inc.