This study investigated the toxic effects of benzene on the liver and kidney functions, complete blood picture, immunoglobulins and some antioxidant enzymes with emphasis of urinary trans, trans-muconic acid (t,t-MA)as a biomarker of benzene exposure, considering the influence of cigarette smoke. Eighty one workers (61 males and 20 females) have been exposed to benzene, while 83 subjects (55males and 28 females) represent a control group were also included. Blood samples were taken for the determination of alanine aminotransferase (ALT), asparatate aminotransferate (AST), Gamma glutamyl transferase (GGT), and alkaline phosphatase (ALP). Beside the determination of both urea and creatinine. Immunoglobulins (IgG, IgA and IgM), Malondialdehyde(MDA)and antioxidants enzyme (SOD and catalase) were estimated. Also the urinary t,t-MA was determined by high performance liquid chromatography (HPLC). Results revealed an increased in the values of the liver enzymes and serum IgM with decreased levels of IgG and IgA. Also an increase in the level of t,t muconic acid and MDA was detected. The levels of blood elements (WBCs, RBCs and platelets), SOD, catalase and GSH were decreased.