In order to determine the involvement of nitric oxide in the pathogenesis of coccidiosis induced by Eimeria, 30 chickens were challenged with mixed sporulated oocysts of four species of Eimeria (E. acervulina, E. maxima, E. necatrix, and E. tenella) at 26 days of age. There was an increasing of oocyst shedding in the infected birds at 6, 10 and 14 days post-infection. Histopathological examination revealed a loss of epithelial tissue, congestion of blood vessels, severe muscular edema and necrosis of submucosa. The sum total of nitrite and nitrate was increased in the serum at 6, 10 and 14 days post-infection progressively, but was only significant (P < 0.05) at 10 and 14 days post-infection compared to earlier days. The nitrate amounts were also significantly higher at days 10 and 14. It can be concluded that infection by four species of Eimeria stimulated NO production after infection. It is therefore possible that NO is involved in the pathogenesis of coccidiosis

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