Abstract: The effect of different concentrations of carbon tetrachloride(CCl4)was studied in theprimary culture of grass carp hepatocytes.As the concentration of 10μl/3×106cells CCl4,the increase of alanine aminotransferase(ALT)and aspartate aminotransferase(AST)as wellas lactate dehydrogenase(LDH) released all from the hepatocytes was observed,and so wasthe increase of the percentage of damaged cells. The adding of sodium selenite(0.2μg/ml)to RPMI-1640 liquid medium and cultured hepatocytes reduced the release of ALT,AST,LDH and the extent of the cell damage.In another experiment evaluating the effect of sodiumselenite and CCl4,grass carp fingerlings were injected intraperitoneally with Na2SeO3 0.1mg/kg.bw each day for three consecutive days, and then with 1ml/kg.BwCCl4.Twenty-four hours later,the relative activity of hepatic superoxide dismutase (SOD)was found to rise 91.5% higher in these fingerlings than those injected with CCl4 only.Sevendays later it was still 54.5% higher.The level of serum ALT decreased gradually.The activitylevel of hepatic lipid peroxide decreased significantly (P 0.05) and that of P-450 increasedsignificantly(P0.01) and so did the contained hepatic microsomal protein(P0.05)inthose fingerlings injected with selenium and then CCl4. Light microscopic observations revealed a decrease of hepatic damage and an increase of nuclear numbers,suggesting that celldivisions might have taken place.It is indicated that sodium selenite may elevate the capacityof hepatic SOD in scavening free radicals,and hepatic counteractions on CCl4 toxicity.