[en] A simple ion exchange procedure has been developed for the separation of chromium from the other chemical elements in biological tissues. This procedure combined with neutron activation analysis has been applied successfully to the determination of chromium in a reference biological material (Bowen's kale). The precision was +-11%, the accuracy 3% and the sensitivity found was 10 ng with only 20 hrs irradiation at a flux of 2.8x10¹³n cm^-2s^-1. The main steps of the procedure are: wet digestion of the irradiated tissue, oxidation to chromium(VI), fixation onto an anion resin in sulphate form, washing of the resin with 1N H₂SO₄, collection of chromium by reductive elution for counting and finally determination of the chemical yield by reactivation. The errors due to interfering elements in the present procedure have been discussed previously. However, the nuclear reaction ⁵⁴Fe(n,α)⁵¹Cr can interfere in the determination of ⁵¹Cr, though its contribution in the analysis of biological tissues should be without importance. Effects of resin overloading are also without importance. Only seven elements are retained considerably on the resin and this fact suggests that the method can be applied to a variety of other matrices which are soluble in sulphuric acid. (T.G.)