Expression of exogenous DNA in vitro is significantly affected by the particular transfection method utilized. In this study, we evaluated the efficiency of two transfection methods, chemically mediated polyethyleneimine (PEI) treatment and physically mediated electroporation, on a rat heart myoblast cell line, H9c2(2-1). After PEI transfection of pPgk-1/EGFP into H9c2(2-1) cells, EGFP expression could be easily detected by fluorospectrometer after 48 h (210 +/- 12 RFU) and continued to increase after 72 h (243 +/- 14 RFU). However, when H9c2(2-1) cells were transfected by electroporation (200 V, 500 mu F, and one pulse), low level EGFP expression was observed after 48 h (49 +/- 4 RFU) or 72 h (21 +/- 14 RFU). In contrast, the easily transfectable control CHO-K1 cell line displayed a stronger EGFP expression than the H9c2(2-1) cells either by PEI or electroporation transfection. When transfection efficiencies were assayed by flow cytometry after 72 h, 13.6 +/- 2.2% of PEI and 10.1 +/- 1.5% of electroporation (250 V, 500 mu F, and two pulses) transfected cells of H9c2(2-1) expressed EGFP, and PEI-transfected cells appeared to be less damaged (viability 93.6%) as compared to electroporation-transfected cells (39.5%). However, both PEI and electroporation (580 V, 50 a"broken vertical bar, and 50 mu F) were effective for transfection of CHO-K1 with a higher efficiency, cell viability, and EGFP expression than H9c2(2-1). Our results indicate that the transfection efficiency of different methods varies among cell lines and that PEI is more efficient than electropolation for transfection of H9c2(2-1) whereas both PEI and electroporation are suitable for CHO-K1 transfection.