Fluoride is an essential element for the growth of humans and animals (Nopakun et al., 1989). Besides, this compound is also referred to as tissue poison since it causes damage in bone and visceral tissues. Its toxicity is closely associated with its ionization property (Faccini and Care, 1965; Andersen et al., 1986). Some researchers suggest that fluoride upsets thyroid functions in humans and animals. The effectiveness of thyroid hormone is closely associated with cAMP level in the target organs. Fluoride is the main adenylate cyclase activator. Increase in the activity of adenylate cyclase also results in the increase in cAMP level (Singh et al., 1963; Burge, 1970; Varner et al., 1998). The study was taken up to assess the effect of high doses of fluoride on thyroid hormones.