Modification of the chemical composition provides a simple, but powerful approach in tailoring the properties of hydroxyapatite (HAp). New procedures now need to be established for measuring the characteristics of OH- groups within HAp and related oxy-HAp. The first step requires a new reliable technique for measuring OH- content in HAp. The quantification of the hydroxyl content will provide a useful tool to further characterize HAps for biomedical applications and allow finer refinement of properties to produce a HAp with the desired properties for implantation. Four different thermal gravimetric analysis approaches were used. The most suitable technique for assessing the hydroxyl content involves the use of calcium pyrophosphate or calcium fluoride with hydroxyapatite.