11 nickel-sensitive subjects were given a gradually increasing daily oral intake of NiSO4 in water. The treatment lasted from between 49 and 152 days and the total intake ranged from 56.43 to 271.70 mg of Ni++. Ni serum concentrations were repeatedly assayed. While the values varied irregularly in the first assessments, they then tended to diminish and to be lower than those found at basal level. The ratio of Ni serum concentration to oral intake demonstrated that, as the doses administered increased, the absorption of nickel decreased. We hypothesize that this trend might be due to an intestinal adaptivity that reduces nickel absorption.