Summary:-Non domestic birds are useful as bioindicators of environmental pollution because they are often at the top of food chain, ubiquitous, and many are abundant and common, making collecting possible. These birds have the advantage of being large, wiThis study was carried on cattle egrets which were collected from sharkia province to determine the level of pesticide residues in their tissues and eggs.I- The organochlorine residues in tissues and eggs of cattle egrets:2. livers : Analysis of organochlorine residues in liver samples revealed that the mean concentrations of α-HCH, β-HCH, p,p’-DDE, dieldrin and endrin were 111.78, 33.99, 53.64, 63.71 and 2. Abdominal fats: The abdominal fat samples from investigated cattle egrets had α-HCH, β-HCH, o,p’-DDT, p,p’-DDE, endrin and heptachlor epoxide residues with amean values of 11.16, 74.55, 7.22, 8.69, 696.03 and 102.35 ng/g wet weight, respectively. WhileBy comparing the residue of organochlorines in tissues and egg yolks of cattle egrets, it was observed that the levels of all detected organochlorines in egg yolk samples are higher than those found in liver and abdominal fat tissues. It was also found thII. The residue of pyrethroids in tissues and eggs of cattle egrets:Estimation of the pyrethroidal residues in liver, abdominal fat and egg yolk samples of cattle egrets revealed that all analyzed pyrethroidal compounds (tetramethrin, cyhalothrin, permethrin and cypermethrin) were not detected in any of examined samples eThe second part of this study was carried out to elucidate the toxic effect of the synthetic pyrethroid (fenpropathrin) on chromosomes of bone marrow cells and some biochemical parameters in serum of albino rats.Thirty mature albino rats were divided into three groups each group contain 10 rats. The first and second group administered fenpropathrin orally at a dose of 150 LD50 (1.4 mg/kg b.wt.) and 1100 LD50 (0.7mg/kg b.wt.), respectively for 14 consecutive day