A simple method for determining histamine and polyamines in various tissues was devised. The method, however, could not be applied to calcified tissues, because the high concentration of Ca" in the extract interferes with the chromatographic separation of these amines. By treating the extracts from calcified tissues with K2CO3, we succeeded in removing the Ca2+, and the method could then be applied to determine the amines in bone tissues of mice. By using this method, we examined the contribution of mast cells and histidine decarboxylae (HDC) to the amount of histamine in the bone. The results indicate that (1) the HDC activity in the bone is the highest among the tissues of normal mice, and the histamine produced by the HDC in the bone is metabolized rapidly; (2) a major part of HDC in the bone is present in the bone marrow cells other than mast cells, and most of histamine in the bone is attributable to the histamine pooled in mast cells; (3) mast cells in the diaphysis are located largely along the endosteal lining; and (4) the method devised in this study may be useful for studying the roles of histamine (or mast cells) and polyamines in calcified tissues.