The present in vitro study was conducted to examine how glutamine influences the lymphocyte function. Glutamine had no effect on the production of interleukin-1 beta, interleukin-6 or tumour necrosis factor-alpha, but influenced the production of interleukin-2 and interferon-gamma. Glutamate, leucine, isoleucine and valine (substrates for glutamine production), or the combination of glutamate and leucine, did not influence the lymphocyte proliferative response or the cytokine production. In conclusion, glutamine influenced the production of some T-cell-derived cytokines, and is thereby important for optimal lymphocyte proliferation. Furthermore, the results show that lymphocytes are not capable of producing glutamine.