The aim of this study was to compare the effect of cyanamide (CNM) and sodium nitroprusside (SNP) on nitrite (NO2-) and nitrate (NO3-), stable metabolites of nitric oxide (NO), serotonin (5-HT), tryptophan (Trp), and lipid peroxidation (TBARS) levels in rat brain. Twenty-four male Wistar rats (350 g) were used, divided in 3 groups of 8 animals each. Control group I received 0.9 % NaCl, CNM (40 mg/kg) was administered to group II, and SNP (20 microg/kg) to group III; all animals received a single intraperitoneal dose. The animals were sacrificed by decapitation and the brain was homogenized to measure the NO2-, NO3-, 5-HT, and Trp levels by liquid chromatography, and TBARS levels by spectrophotometry. NO2- levels significantly increased (p< 0.01) in the CNM group, while 5-HT and TBARS significantly increased (p = 0.001) both in SNP and CNM groups in relation to the control group. Trp levels presented a slight increase in the CNM group with respect to the control group. The results suggest that free radicals (Nitroxyl and NO) generated by CNM and SNP, respectively, are responsible for oxidative stress induced in brain.