Pesticide have been used extensively for agricultural. domestic and industrial purpose (Hayes and Laws, 1991). Pyrethroid insecticides are synthetic analogues of the natural pyrethrins contained in flowers of genus Chrysanthemum (Leahey,
1985). In recent years. pyrethroids have been used widely due to their good insecticidal activity and low mammalian toxicity (Hutson and Roberts, 1985). However. their wide spread use. their high nonselective potency and their considerable stability in the environment make them potentially harmful (Gassner et at, 1997). In addition.
they are commonly used in mosquito repellents to protect the human population. either by impregnating bednets with pyrethroids (Huailu et al., 1995) or in the form of vaporizing mats. coils. scented sticks and liquidators (Miyamoto and
Kearney, 1983; Warui, 1992). Because these repellants are used routinely overnight.
it may allow human to inhale vapors that may be harmful especially to children due to the immature blood - brain barrier (BBB) and metabolic inefficiency compared to adults (Sheets et at, 1994). Several experimental studies demonstrated
that young mammals were generally more sensitive than adults to the acute toxicity of insecticides (Pope and Liu, 1997; Moser and Padilla, 1998). However. very few studies have evaluated age· related differences in response to chronic exposure to lower doses of these insecticides. Eriksson (1997) proved that low - dose exposure to both persistent and non-persistent environmental agents. e.g. pyrethroids, nicotine and paraquat. during the neonatal growth spurt period could lead to functional abnormalities of the brain during adulthood. Encephalopathies in children have been reported following the use of insect repellent containing Ienvalerate. which is a pyrethroid pesticide (Garrettson, 1997; Osmitz and Murphy, 1997). Studies of  Gupta et at (1999) exhibited a significant effect of pyrethroid pesticides on BBB, liver and kidney functions. Changes in the BBBpermeability (Srinivas et al., 1993), free-radical generation and oxidative stress (Bagchi et at, 1995) as well as affection of mitochondrial and microsomal function (Yamano and Morita, 1995) are amongIhe suggested mechanisms by which these pesticides may exert their toxicity. The aim of this work is to study the possible histological changes and their reversibility that may occur in the liver of the adult and growing male albino rats following chronic inhalation of commercially available pyrethroid-containing mosquito repellent mats (Ezalo mats).