The effect of different sublethal concentrations of diazinon at 1, 2 and 4 mg/L on some hematological and biochemical parameters of grass carp (Ctenopharyngodon idella) weighing 850±155g was studied after 1, 7, 15, 30 and 45 days post exposure to the toxicant as a bath for 12 hours at 18-22 C. In one day exposure fish to the toxicant, the values of neutrophiles exposed to 2 and 4mg/L were significantly higher than control fish, while lymphocyte and monocyte counts in fish exposed to 2 and 1mg/L were significantly lower than control one (P0.05). Seven day after exposing fish to the toxicant, values of WBC in all experimental fish were significantly higher than control fish, while level of neutrophiles in fish exposed to 1mg/L and values of lymphocytes in fish exposed to 2 and 4mg/L were significantly higher and lower than control fish, respectively. Also, values of ALT, AST and ALP in all experimental fish were significantly lower, higher and lower than control fish, respectively (p0.05). Forty five days post-exposing fish to the toxicant, the values of WBC and heterocytes in all experimental fish were significantly higher than control one, while levels of lymphocytes, ALT and ALP were lower than control fish (p<0.05). Also, the level of AST in fish exposed to 4mg/L and level of LDH in fish exposed to 1 and 4 mg/L were significantly lower than control fish (p<0.05)
