We examined the effects of fluoride intoxication on certain blood plasma biochemical indices in rats. Forty-eight adult female Wistar rats weighing 123-142 g were divided into eight groups: two control groups (0 and 28 days) and six experimental groups, namely sham-injected animals (vehicle), injected with pineal proteins (PP) and melatonin (Mel), intoxicated with fluoride (F), and also F+PP and F+Mel groups. Fluoride (150 ppm, per os administration with drinking water), melatonin (10 mg/kg, i.p.), and PP (100 mu g/kg, i.p.) were administered daily for 28 days. Blood samples were collected at the end of experiments to estimate plasma [Na(+)] and [K(+)], alkaline phosphatase (ALP) activity, and levels of glucose and proteins in different animal groups. The plasma [K(+)] and [Na(+)], and ALP activity were significantly (P < 0.05) elevated in F-treated animals, as compared with others. Administration of PP and Mel in F-treated rats caused significant (P < < 0.05) reduction of [Na(+)], [K(+)], and ALP levels. Interestingly, PP and Mel administrations resulted in noticeable (P < 0.05) increases in the plasma glucose level in F-intoxicated animals, as compared to other groups. These findings convincingly indicate that PP and Mel exert ameliorative effects on fluoride-induced adverse changes in certain biochemical parameters in rats.