abstract–The effect of calcium hydroxide as a potential bone inductor in ectopic locations was studied by implanting calcium hydroxide subcutaneously or intraperitoneally in rats. The calcium hydroxide was either left in direct contact with the host tissue or separated from it by Millipore® filters. The observation periods ranged from 6 to 18 weeks. The present investigation could not verify previous reports of calcium hydroxide as a bone inductor when placed in ectopic locations. However, in some of the cases where direct contact was established between host tissue and calcium hydroxide, marked hyperplasia of the connective tissue and numerous multinuclear giant cells were observed. Occasionally some ill‐defined basophilic, von Kossa positive islands were observed which slightly resembled immature bone. If direct contact between calcium hydroxide and the host tissue was prevented by Millipore filters, no significant reactions were observed in the host ti