In the present study, continuous infusion of 5 and 25 mg·kg−1·day−1of L-NAME significantly decreased TNF-α and IFN-γ production by T-leukocytes and 50 mg·kg−1·day−1of L-NAME significantly increased TNF-α production by splenic macrophages and IFN-γ and IL-2 production by T-splenocytes in rats with sub-acute peritonitis. The gene discussed is TNF; the disease is peritonitis.