Nickel (Ni2+) elicits production of functionally distinct cytokines in vitro, but the relation between the cytokine profile and the degree of the allergic reaction in vivo needs to be better defined in order to improve the understanding of the immunological mechanisms involved in contact allergy and to facilitate development of in vitro diagnostics. The aim of the study was to define Th1-type [interferon-gamma (IFN-gamma)], Th2-type [interleukin-4 (IL-4), IL-5 and IL-13] and regulatory (IL-10) cytokine responses to Ni2+ in peripheral blood mononuclear cells (PBMC) from subjects with varying patch test reactivity to Ni2+. The study included subjects with strong (+3), moderate (+2), weak (+1) or negative (controls) patch test reactivity to Ni2+ (n = 10 per group). All +3 and +2 subjects but only three +1 subjects had a clinical history of contact allergy to Ni(2+). Cytokine production of PBMC stimulated with Ni(2+) was determined by enzyme-linked immunospot and/or enzyme-linked immunosorbent assay. Ni2+ elicited significant production of all cytokines in PBMC from patch-test-positive subjects versus controls with a positive correlation between each cytokine and the patch test reactivity as well as with other cytokines. More subjects responded to Ni2+ above cut-off values with Th2-type cytokines as compared with IFN-gamma or IL-10; 100% of +3, 80% of +2, 50% of +1 and 0% of control subjects displayed reactivity to Ni2+ based on IL-4 and IL-13 assays. Despite the prevailing view of Ni2+ allergy as a type-1-mediated condition, the in vivo reactivity to Ni2+ correlated with a mixed Th1-type, Th2-type and regulatory cytokine response to Ni2+in vitro. The results accentuate the importance of type 2 responses in contact allergy and also demonstrate that IL-4 and IL-13 are reliable markers for Ni2+ allergy.