Ascites syndrome results in significant economic losses to the broiler industry due to high mortality around the world especially in major poultry-producing countries. Environmental conditions such as high altitudes trigger the development of ascites syndrome, which is characterized mainly by hypoxemia. The physiology of this syndrome has been studied extensively. It is generally accepted that hematological characteristics play an important role in the pathophysiology of ascites in chickens. The present study was conducted to examine the physiological and histological trend of blood tissue in ascitic trend at two regions with different altitude, Shahr-e-kord (1850 m above sea) and North of Iran (sea level). For this purpose two samples of 120 male broilers (Ross 308) were assigned in each of two regions for 6 weeks. On weekly intervals body weight and blood samples were drown on individual basis. Part of sample was stored at 4 ? C ْ pending hematocrit, red blood cell count and hemoglobin analysis while the reminder was centrifuged at 5000 rpm for 10 min to obtain plasma, which was stored at -20 ? C ْ pending for further analysis. Analysis of all data was done with using GLM procedure of SAS. Result showed that at 4 wk of age, Shahrekordian broiler exhibited an significant increase (P 0.01) in hematocrit, red blood cells count and hemoglobin concentration with no significant change in mean corpuscular value. Increased blood cell production in Sharokordian broiler was matched by an increase (P 0.01) in the proportion of immature blood cells. Hematocrit in Northern broiler was not significant between weeks except at 2 wk of age. RBC count was significantly different at 6 wk of age, the difference could be due to increase of red blood cells as increased age. Comparison of hematological characteristics at every week in two regions showed that hematological parameters were significantly higher in Shahrekordian broiler as compared to Northern broilers at 4 week of age. Biochemical analysis was not significant between weeks in both. It could be concluded that hematological parameters can be used to show some of physiological difference between broilers reared in different regions and onset of ascitic trend
