Nickel sulphate is the most frequent cause of allergic contact dermatitis, determined by patch test at a frequency of 13% in the German population, and expected in the general adult population in 10%. Women are over-represented in patch test-positive individuals with a frequency of 20% as compared to 6% in men. ELISpot assay could be used with nickel chloride to stimulate cytokine production. ELISpot is more convenient and a suitable test, especially for monitoring in clinical studies, e.g. on the desensitization/ tolerance induction by oral nickel application.