AbstractWe describe a method for the histochemical localization of acid phosphatase (AcP) activity in sections of paraffin embedded bone, following demineralization in ethylene diamine tetra acetic acid (EDTA). AcP activity is consistently demonstrated as a bright red color in cells after incubation in naphthol phosphate/hexazotized new fuchsin substrate. Because this method has been used to demonstrate AcP activity in human and animal tissues, it has applications in both diagnostic and research areas. It is well suited to smaller laboratories because no expensive resins or specialized microtome equipment are needed. Furthermore, the time required for complete decalcification is often shorter than that required to process the same tissue into a suitable resin block. (The J Histotechnol 13:189, 1990)