Trypanosomiasis remains a major public health problem to man over much of tropical Africa. The disease is caused by protozoan parasites of the genus Trypanosoma and is fatal if untreated. The effects of T.b.brucei infection on plasma melatonin concentration and pineal gland histopathology was investigated in male albino rats. Twelve rats were each infected intraperitoneally with 0.2ml of infected blood containing approximately 1.0 x 10 4 live T.b.brucei parasites. Twelve other rats served as

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... nfected controls. Trypanosomes were detected in the blood of infected rats 5-8 days post-infection. There was a significant difference (P=0.0382) in plasma melatonin concentration between control and experimental rats. Histopathological changes in the pineal gland of experimental rats included tissue degeneration and pinealocytes with pyknotic nuclei. These histopathological changes were responsible for the decrease in plasma melatonin concentration in the experimental rats.