Magnesium-substituted hydroxyapatites (HAP) have been prepared to evaluate the influence of cationic substitution on the surface basic properties of HAP. Despite successful introduction of some of the magnesium cations into the HAP structure (as evidenced by XRD, infrared, and Raman), no influence of low magnesium content in Mg(x)-HAP samples (x <= 1) on the basic conversion of 2-methylbut-3-yn-1-ol was found, which can be explained by the surface content of magnesium being low, as evidenced by CO adsorption. At higher magnesium content, a higher amount of magnesium could be detected on the surface, but this resulted in a structural disorder leading to either nonstoichiometry or eventually the formation of the phase whitlockite. In this case, the associated relative decrease of the amount of basic sites, as well as the possible influence of the enhanced surface concentration of acidic POH groups, are responsible for the lower intrinsic basicity of the related samples. In contrast, preliminary results indicate that an enhancement of the basic reactivity is observed on substituting calcium for strontium.