This cell line is established from Mouse Swiss NIH embryo.These cells are sensitive to sarcoma virus focus formation and leukemia virus propogation. Cells have now lost their contact inhibition. These cells are useful for DNA transfection and transformation studies; tested and found negative for ectromelia virus (mousepox). Fetal calf serum is no suitable. The serum initially employed and found to be satisfactory was from the Colorado Serum Company.