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Cypermethrin is a synthetic pyrethroid that belongs to a group of insecticides with low mammalian toxicity but high insecticidal activity. The present study was undertaken to evaluate subacute toxicity of orally administered cypermethrin in rats based on the haematological, enzymological, and histological brain examination. The study was conducted on 8-week old male Wistar rats and Kral 250 EC (250 g of cypermethrin/l) was orally administered (60, 150, and 300 mg/kg) for 28 consecutive day. Thus, the investigation covered four groups of animals: three experimental groups and one control group, of 20 rats each. Our results demonstrated that experimental groups receiving both 150 and 300 mg/kg cypermethrin treatment led to significant dose–dependent decrease in some haematological parameters [red blood cell (RBC) counts, haematocrite (Ht), thrombocyte, and mean corpuscular haemoglobin (MCH) values] at the end of the experiment. When compared with control animals, there were significant increases between initial body weights and final body weights of cypermethrin treated rats, but there was a significant decrease in brain/body weight ratio of the animals of all treated groups. Furthermore, there was no statistical difference between control group and all experimental groups for brain acetylcholinesterase (AChE) and blood cholinesterase (ChE) enzyme activities, although brain AChE activities were increased in rats treated with a dose of 150 and 300 mg/kg cypermethrin. Histologically, some deformation areas due to ischemia and pyknosis of the cytoplasm of the neurons were observed in brain tissues of rats treated with all doses of …