The aim of the study was to assess the effect of two major groups of hypolipemic drugs, HMG-CoA reductase inhibitors (statins) and PPARalpha activators (fibrates), on the secretory function of T-lymphocytes in patients with primary type II dyslipidemia. Sixty-three patients with type IIa dyslipidemia were randomized to fluvastatin (40 mg daily; n = 33) or simvastatin (20mg daily; n = 30), while 68 type IIb dyslipidemic patients were treated with micronized ciprofibrate (100mg daily; n = 34) or micronized fenofibrate (200mg daily; n = 34). Lipid profile and cytokine (interferon-gamma and interleukin-2) release by phytohemagglutinin-stimulated lymphocytes were determined at the beginning of the study and after 30 and 90 days of treatment. Compared to healthy subjects (n = 59), both type IIa and IIb dyslipidemic patients exhibited higher baseline release of interferon-gamma and interleukin-2. Fluvastatin, simvastatin and, to a less extent, ciprofibrate and fenofibrate inhibited the release of both cytokines, but this effect did not correlate with their lipid-lowering potential. Hypolipemic agents also slightly reduced plasma interleukin-2 levels. Our study suggests that the beneficial effect of hypolipemic drugs involves their inhibitory action on the secretory function of T-lymphocytes. This lipid-independent action is stronger for statins than for fibrates and probably results from their "class" effect. The treatment-induced reduction in the release of both cytokines may contribute to the clinical effectiveness of statins and fibrates in the therapy of atherosclerosis and in the management of organ transplant recipients.