Major advances in dissecting mechanisms of NO-induced down-regulation of the anti-tumour specific T-cell function have been accomplished during the last decade. In this work, we studied the effects of a NO donor (AT38) on leukaemic Jurkat cell bioenergetics. Culturing Jurkat cells in the presence of AT38 triggered irreversible inhibition of cell respiration, led to the depletion of 50% of the intracellular ATP content and induced the arrest of cell proliferation and the loss of cell viability. Although a deterioration of the overall metabolic activity has been observed, glycolysis was stimulated, as revealed by the increase of glucose uptake and lactate accumulation rates as well as by the up-regulation of GLUT-1 and PFK-1 mRNA levels. In the presence of NO, cell ATP was rapidly consumed by energy-requiring apoptosis mechanisms; under a glucose concentration of about 12.7mM, cell death was switched from apoptosis into necrosis. Exposure of Jurkat cells to DMSO (1%, v/v), SA and AT55, the non-NO releasing moiety of AT38, failed to modulate neither cell proliferation nor bioenergetics. Thus, as for all NSAIDs, beneficial effects of AT38 on tumour regression are accompanied by the suppression of the immune system. We then showed that pre-treating Jurkat cells with low concentration of cyclosporine A, a blocker of the mitochondrial transition pore, attenuates AT38-induced inhibition of cell proliferation and suppresses cell death. Finally, we have studied and compared the effects of nitrite and nitrate on Jurkat cells to those of NO and we are providing evidence that nitrate, which is considered as a biologically inert anion, has a concentration and time-dependent immunosuppressive potential.