Organophosphate compounds are very toxic chemicals and used in widespread applications. The present study was designed to examine the role of exogenous melatonin against organophosphate toxicity in tissues (brain, heart, jejunum, kidney, liver, lung, muscle and pancreas) trace and major element levels of rats. Trace and major element concentrations in the tissues were measured in the sham group, the control group, prophylaxis with the melatonin group and therapy with the melatonin group (TM) by inductively coupled plasma-optical emission spectroscopy. Statistically significant differences among the experimental groups were detected for some tissue trace and major element concentrations. In the brain tissue, the Al, Mn and Se concentrations in the sham group were significantly higher than those in the control group (p < 0.05). In the heart tissue, the Cu, Mn and Se concentrations in the sham group were significantly increased than those in the control group (p < 0.05). In the kidney tissue, trace and major element concentrations in the TM group were significantly lower than those in the sham group (Fe and Mn; p < 0.05, Cu, Mo, Ni, Ti, V and Zn; p < 0.01). In the liver, Mg, Al, Zn and Ca concentrations in the TM group were significantly higher than those in the fenthion-treated control group (p < 0.01). In the muscle tissue, element concentrations in the TM group were significantly lower when compared with the sham groups (Ca and Si; p < 0.01). The Al, Cr, Mo, Ni, Si and Zn element concentrations were markedly decreased in the control group as compared with the TM group in the pancreas tissue (p < 0.01). In conclusion, according to the results of the present study the major findings are that the fenthion-treated rat's tissue element levels were effected and the melatonin may normalize the altered levels of some trace and major elements of the tissues in organophosphate toxicity. (C) 2009 Elsevier Inc. All rights reserved.