A detailed description of a simple technique for acid phosphatase demonstration in osteoclast cells is presented. The method is short, relatively uninvolved and allows the use of undecalcified bone sections. All materials and chemicals used are commercially available. The sections were stained histochemically using naphthol AS-B1 phosphoric acid as a substrate and counter stained with Mayer's Haematoxylin. Sections prepared by this method showed good results and enabled accurate measurement of osteoclast counts.