Objective:To investigate the cellular toxicity of isoniazid together with rifampicin and the metabolites of isoniazid on cultured QSG-7701 cells lines.Methods:Isoniazid,rifampicin, mixture of rifampicin and isoniazid,acetylhydrazine,hydrazine were added in cultural media of QSG-7701 cells and cultured for 48 hours.The survival rate of cells was determined by MTT method.The cultural media and cells were collected and the activity of lactate dehydrogenase was detected by chromatometry.Results:Compared with control group,the survival rate decreased significantly and the lactate dehydrogenase released from cell increased significantly in cells treated with isoniazid,rifampicin,acetylhydrazine,hydrazine.Hydrazine,the metabolite of isoniazid produced significant damage on hepatocytes in low concentration.Conclusions: Rifampicin together with rifampicin and metabolites of isoniazid produce cellular toxic effects and hydrazine may be the most toxiferous metabolite. Objective: To investigate the cellular toxicity of isoniazid together with rifampicin and the metabolites of isoniazid on cultured QSG-7701 cells lines. Methods: Isoniazid, rifampicin, mixture of rifampicin and isoniazid, acetylhydrazine, hydrazine were added in cultural media of QSG-7701 cells and cultured for 48 hours. survival rate of cells was determined by MTT method. cultural media and cells were collected and the activity of lactate dehydrogenase was detected by chromatometry. Results: Compared with control group, the survival rate decreased significantly and the lactate dehydrogenase released from cell increased significantly in cells treated with isoniazid, rifampicin, acetylhydrazine, hydrazine. Hydrazine, the metabolite of isoniazid produced significant damage on hepatocytes in low concentration. Conclusions: Rifampicin together with rifampicin and metabolites of isoniazid produce cellular toxic effects and hydrazine may be the most toxiferous metabolite.