Nitric oxide (NO) is known to be implicated in various renal diseases induced by lead poisoning and recent works have shown the effect of some antioxidants in reducing the toxic effects of lead. Melatonin is attractive for its direct and indirect antioxidant effects; furthermore it is naturally produced in mammalians, including humans. Recently, it has been shown that melatonin attenuates the toxic effects of sub-acute lead intoxication in kidneys without altering NO metabolites concentration. This work demonstrates the use of nickel tetrasulfonated phthalocyanine/polyphenol-modified ultramicroelectrodes to monitor in vivo and in situ changes of NO within rat kidneys. NO itself was detected directly and in real-time inside the kidney of lead and melatonin treated rats after induction by L-arginine. The results indicate that NO production decreases in lead treated rats, likewise in co-treated with melatonin rats. In addition, melatonin administration did not affect the production of NO respect to the control. By means of these experiments was verified that melatonin does not alters NO production in kidneys during sub-acute lead intoxication. (C) 2015 Elsevier Ltd. All rights reserved.