The results of this study indicate that melatonin induces hypothyroidism in mice within eight days. Simultaneous administration of melatonin and petroleum ether extract of Commiphora mukul brings about a significant improvement in thyroid structure and function. Further, melatonin induced hypothyroidism is although a little reversible yet it is normalized quickly after C. mukul treatment. These data suggest that C. mukul directly stimulates thyroid function probably through some enzymatic mechanisms.