Plasma chemistry and haematological studies were conducted on chickens with coccidiosis. Male White Leghorn chickens, of two weeks old, were inoculated with 5 x 104 Eimeria tenella sporulated oocysts or with 1 x 106 E acervulina sporulated oocysts. Blood samples were taken four, seven and 11 days after inoculation. A wet chemistry system was applied to measure the plasma activities of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, gamma glutamyltransferase, creatine kinase, amylase and lactate dehydrogenase and the concentrations of creatine, total biirubin, urate, total cholesterol, total protein, albumin, glucose and triglycerides. A dry chemistry system was applied to measure sodium, potassium, chloride and calcium. The number of red blood cells and packed cell volume were determined by a micro cell counter and blood pH was measured with a blood gas analyser. The erythrocyte count, packed cell volume, sodium and chloride levels in the chickens infected with E tenella were significantly (P<0.05) lower than those of the uninfected controls. The significant decrease in blood pH of the chickens infected with E acervulina suggests malabsorption associated with duodenal lesions induced by the infection.