To investigate the influence of different transfected cells using expression studies of dysfunctional factor VII variants, we expressed recombinant FVII using COS-1 cells, CHO-K1 cells, BHK cells and HEK293 cells. The mutant type F7 DNAs with Leu-48Pro in the prepeptide domain, with Ser126Phe in the EGF-2 domain and with Gly354Cys in the catalytic domain were transfected in the four kinds of cell lines. Additionally, FVII Ser126Tyr and Ser126Gly were expressed to investigate different substitutions from Phe in position 126 in FVII. The FVII:Ag of recombinant FVII Leu-48Pro in conditioned medium, which were expressed in COS-1 cells, CHO-K1 cells, BHK cells and HEK293 cells, were 37.9% 68.0%, 11.7% and 9.2% respectively, when wild-type FVII was defined as 100%. The levels of FVII:Ag in cell lysates were 26.2%, 44.9%, 25.6% and 50.5%, respectively. The FVII:C of recombinant FVII Gly354Cys in conditioned medium were 3.7%, 3.5%, 1.5% and 1.7%, respectively. The levels of FVII:Ag were similar to FVII:C. The FVII:C of both recombinant FVII Ser126Phe and Ser126Tyr in conditioned medium of all four cell lines were considerably lower than that of FVII wild type. However, levels of FVII:Ag in conditioned medium of recombinant FVII S126G were 86.8% on COS-1 cells, 14.1% on CHO-K1 cells, 28.3% on BHK cells and 114.6% on HEK293 cells. When carrying out expression studies for FVII mutation, we have to consider different results based on the patient's laboratory phenotype when using different kinds of transfected cells.