The assay of traces of cobalt 60 by the method of recording spectra, using a one canal gamma spectrometer, has been completely investigated. The interferences due to iron 59 and cobalt 58 have been studied in detail. A method is described for the direct assay (without dissolution or separation) of cobalt in inconel by activation by thermal neutrons. This determination can still be effected readily on only 0,1 mg of this alloy. The method is rapid, simple and sensitive.