The alkaline phosphatase used for this product is isolated from calf intestine. The very high specific activity of this enzyme is retained during our biotinylation procedure. Biotinylated alkaline phosphatase used in conjunction with Avidin D provides one of the most sensitive enzyme detection systems available. For some solid-phase assay systems, the use of biotinylated alkaline phosphatase provides a more sensitive system than the Avidin D conjugate. This enzyme also offers a potential for use as a second marker in immunohistochemical staining.