Nickel is the major cause of metal-induced allergic dermatitis. Twelve nickel-specific T cell clones were used to investigate the cellular immune reactions occurring in nickel sensitivity. The selection between the alternative T cell receptors alpha beta and gamma delta and two alternative V beta genes (V beta 5 and V beta 8) were studied to see if nickel induces a selective pressure for clones bearing particular genes. Cell surface markers were studied by monoclonal antibodies and flow cytometry. Soluble mediators were measured by an ELISA method. The clones used T cell receptor alpha beta genes but did not use V beta 5 or V beta 8. They were T helper clones with a primed memory marker (CD3+ CD4+ CD8- CD45RO+) and carried HLA-DR. None of the clones secreted IL-1 alpha, all of them secreted IL-2 receptor. Four clones secreted IL-1 beta, six IL-4 and seven IL-6, the peaks in IL-2R and IL-6 secretion preceding IL-4 secretion. The clones helped immunoglobulin synthesis. The clones from late effector phase of the nickel allergic reaction favours the use of T cell receptors alpha beta genes. Nickel-specific clones were phenotypically indistinguishable but differed in soluble mediators produced.