The heat of immersion and surface properties of hydroxyapatite initial and modified (containing Ca, P, and CO32-) and composites with fumed oxides were examined using microcalorimetry. The microcalorimetric measurements showed a regular decrease in the heat of immersion in water per area unit with an increase in the specific surface area of samples. The nitrogen adsorption/desorption isotherms were used to estimate the textural characteristics of the materials studied.