Inter-action of alanine, aspartic, boric, citric, glutamic, lactic, malic, malonic, succinic and valine with hydroxyapatite at pH 4.0 and 7.3 shows no evidence for adsorption of these anions by the hydroxyapatite, except for citric acid, when investigated by infrared analysis of their strongly adsorbing ionic carboxylic acid groups.