The assay of cobalt in 18/8 steel by activation may be effected on a 1 mg. sample if one has available a flow of 10¹³ neutrons/s/cm² for a period of 15 hrs. Iron interferes, as it gives rise to γ rays which superpose on those of ⁶⁰Co; it is separated by ion exchange on resin. The formation of radiocobalt 58 from nickel prevents the assay of cobalt in steel by determination of the total activity. The final determination is therefore carried out on the γ spectrum. Three methods are proposed: the first is based on the determination of cobalt by application of the activativation formula, the second uses an external standard and the third uses ⁵⁸Co as internal standard. The sensitivity, precision, advantages and disadvantages of each technique are discussed. This method of assay is very rapid if one disregards the time of activation and that of the ‘cooling’ necessary for elimination of short period isotopes.