Nickel is one of four ferromagnetic elements (symbol Ni, at. Num. 28). Several enzymes depend on nickel for activity, including some ureases, carbon monoxide dehydrogenases (methane forming enzymes which reduce CO? to CH?) and some hydrogenases which allow the production or removal of H2. Most of these activities are found in the archaebacteria. Nickel forms complexes with sulfhydryl compounds with significant absorbance in the UV/visible region in the presence of other ions. BioVision's Nickel Assay kit provides a simple method of quantifying Ni2+ in a variety of samples. The assay takes advantage of reaction of Ni2+ with mercaptoethanol in borate buffer to form a complex with strong absorbance bands from ~300 to 600 nm. Fe2+ and Co2+ inte