Used in histology and pathology to detect acid phosphatase enzyme activity in tissue sections, particularly to identify osteoclasts in bone tissues and to differentiate certain types of leukemia. The lead nitrate method forms an insoluble lead phosphate precipitate at the site of enzyme activity, which appears as a dark deposit under the microscope. This staining technique is especially valuable in diagnosing diseases involving abnormal bone resorption and in characterizing tartrate-resistant acid phosphatase (TRAP) positive cells, such as in hairy cell leukemia. The method provides high localization precision at the cellular level, making it useful for research and clinical diagnostics.