Non-thermal dielectric barrier discharge plasma is now being widely developed for various medical applications such as skin sterilization, blood coagulation, induction of apoptosis in malignant tissues, and wound healing among others. In this paper, we investigate the toxicity of non-thermal plasma treatment on endothelial cells, which line all blood contacting surfaces in the body. Our initial results indicate that low power non-thermal plasma is relatively non-toxic to endothelial cells at short exposure times up to 30 s, while non-thermal plasma treatment at longer exposure times is cytotoxic. Non-thermal plasma at shorter exposure times may induce proliferation in the cells.