The 3T3 cell line was established from 17 to 19 days old mouse embryos. The cells are established from disaggregated Swiss albino mouse embryos in 1962; cells are used for transfection studies with DNA viruses and as assay system for transformation studies; cells have a high sensitivity to contact inhibition. A confluent monolayer yields 40.000 cells/cm2. The cells should be grown in plastic flasks; they do not grow well on some types of glass surfaces. A saturation density of approximately 50.000 cells/cm2 can be reached. The species was confirmed by Real-Time PCR.