Persistence and biochemical characteristics of cypermethrin and permethrin in the blood of male rats were studied following oral administration of a single dose containing 10 mg kg-1 of holy weight of each pyrethroid. The highest residue concentrations of cypermethrin (2.38 μg. ml-1) and permethrin (8.83 μg. ml-1) in rat blood tissue were detected 24 h after treatment. After two weeks cypermethrin residues decreased to 0.013 μg. ml-1. whereas permethrin was not detected. Both pyrethroids decreased the red blood cell (RBC) count, and packed cell volume (PCV). The greatest reduction in RBC count and PCV occurred at 504 h and 336 h respectively. Moreover, the result of post treatment white blood cell (WBC) count was influenced more by permethrin than by cypermethrin, especially after 80 h, 168 h and 504 h of treatment. However. the blood haemoglobin concentration in treated rats was not affected by either pyrethroid.