Objective To investigate the expression difference of multidrug resistance and apoptosis related genes and its contribution to mechanisms of multidrug resistance in human lung adenocarcinoma parental cell line A 549 and cisplatin resistant cell line A 549 DDP Methods RT PCR and Immunohistochemical staining were performed to detect the mRNA expressions and protein production of multidrug resistance related protein (MRP),lung resistance protein (LRP),bcl 2,and C erbB 2 in A 549 and A 549 DDP .Results MRP,bcl 2,and C erbB 2 mRNA were expressed in A 549 ,but no LRP mRNA was detected in A 549 MRP,C erbB 2,and LRP mRNA expression levels in A 549 DDP were significant higher than those in A 549 ,otherwise,LRP mRNA was detected in A 549 DDP There was no difference of bcl 2 mRNA expressions between A 549 and A 549 DDP ( P =0 731) Bcl 2 protein expressions were strongly positive both in A 549 and in A 549 DDP MRP protein expressions in A 549 were faint positive,while C erbB 2 and LRP were negative MRP protein expressions in A 549 DDP was median positive C erbB 2 and LRP protein expressions in A 549 DDP were strongly positive Conclusions The heterogenous expression of MRP,C erbB 2,and LRP in A 549 and A 549 DDP may be associated with primary and secondary drug resistance in lung cancer