Ectopic cell transplantation has been studied as an alternative to whole organ transplantation or as a method to produce secretable proteins for genetic disorders. In this study, bone marrow stromal cells isolated from C57Bl/6 mice were genetically modified to express either lacZ- or B-domain-deleted human factor VIII. In vitro modification of the isolated bone marrow stromal cells was initially performed by transducing increased doses of VSV-G pseudotyped lentiviral vectors expressing lacZ. At a MOI of 25, all of the bone marrow stromal cells were X-gal positive, which maintained their ability to expand and differentiate prior to transplantation into mice. Extremely poor engraftment was observed in the liver, but transplantation of the bone marrow stromal cells expressing lacZ under the kidney capsule resulted in long-term viable X-gal-positive cells for at least 8 weeks (length of study). In vitro expression of human factor VIII was detected in a dose-dependent manner following bone marrow stromal cell with a factor VIII-expressing lentiviral vector. Transplantation of the factor VIII-expressing bone marrow stromal cells under the kidney capsule led to long-term therapeutic expression in the mouse plasma (1-3 ng/ml; n = 4-5 mice/group) for 8 weeks. This study demonstrated that ectopic transplantation of bone marrow stromal cells under the kidney capsule can be effective as a method to express secretable proteins in vivo.