A non-destructive method for the determination of hafnium in zircons, based on the formation of 179mHf (half-life 19 sec) is proposed. For a neutron flux of 10⁹ n cm⁻² sec⁻¹ and an irradiation time of 60 sec, the limit of detection is about 1·10⁻⁷ g. The method is rapid and very selective. Results of some hafnium determinations are reported.