The effect of Tetramethrin- and prallethrin-based mosquito repellent pyrethroids on rat platelet membranes of cholesterol, phospholipids, lipid peroxidation in platelet membrane was investigated. Rats were chronically exposed to these compounds by continuous inhalation for 8-10 hours a day for 2-3 months, which entered into circulation and counted changes in membranes of platelets. Platelet membrane fluidity was determined by DPH. Pyrene fluorescence anisotropy experiments revealed that tetramethrin and prallethrin exposure to subjects, compared with controls, induced a significant decrease in platelet membrane fluidity as measured by DPH and pyrene. A significant increase in lipid peroxidation was observed in the subjects exposed to both compounds. A significant decrease in the activitiesof platelet membrane-bound enzymes, viz., total ATPase, Na⁺/K⁺-ATPase and Ca²⁺-dependent ATPase and Mg²⁺-ATPase was also recorded.