Among commercially available urinary human menopausal gonadotrophin (HMG) material, gonadotrophins comprise <5% of the total protein content. Thus, during a typical ovarian stimulation cycle with HMG, several milligrams of non-relevant proteins are administered that may lead to unwanted side effects, including allergic or other hypersensitivity reactions. The effects of two recombinant and four urinary gonadotrophin preparations of different purity upon the function of T cells from healthy blood donors were studied. Only one of the HMG preparations significantly enhanced the spontaneous proliferation of peripheral blood mononuclear cells. Phytohaemagglutinin-induced proliferation was not modified by any preparation, while two preparations significantly increased proliferation in the mixed lymphocyte reaction. Three of the HMG preparations induced the release of interleukin (IL)-1. Highly purified FSH, either urinary or recombinant, showed no effect. None of the preparations induced detectable IL-2 production, whereas only one HMG preparation tended to decrease IL-2 secretion. No major changes in CD25 expression were induced by any of the gonadotrophins. Cytokine measurement by immunoassays detected only IL-1beta in two commercially available preparations. The various effects exhibited by the crude urinary preparations were not a result of the gonadotrophin content and differed from product to product, suggesting that the contaminants present in these preparations are not identical. This could contribute to unpredictable clinical manifestations of allergic or other immune reactions.