Cobalt is a hard, lustrous, grey metal, a chemical element (symbol Co, atomic number 27 and atomic mass 58.9). Cobalt is an essential trace-element for all multicellular organisms as the active center of coenzymes called cobalamins. These include vitamin B-12 which is essential for plants and animals [1]. Cobalt is also an active nutrient for bacteria, algae, and fungi, and may be a necessary nutrient for all life. Cobalt, particularly the Co²ᶧ species, forms complexes with a large number of organic and inorganic molecules with a range of extinction coefficients in the visible range. The BioVision Cobalt Assay kit takes advantage of the reaction of Co²ᶧ with mercaptoethanol in basic media. Under the condition, Cobalt forms a complex with a strong absorbance band at 475 nm. The metal ions Fe²ᶧ, Cu²ᶧ, Ni²ᶧ, Zn²ᶧ, Mn²ᶧ, exhibit less than 10% interference at this wavelength. The kit provides a quick simple accurate method of quantitating Co²ᶧ in a variety of samples.