A diploid, continuous cell line, Golden Hamster Embryo Fibroblast-III (GHEF-III), which had been passaged for one year, was established essentially by a 3T3 protocol from primary culture of 14-day-gestation Golden Hamster embryo fibroblast cells. The cultured fibroblast exhibited monolayer growth and had contact inhibition. In morphological identification by light microscope (LM), transmission electron microscope (TEM) and immunofluorescence examination (IF), these multipolar and spindle-shaped cells had a large ovoid nucleus, enriched rER and mitochondria in the cytoplasm. On the other hand, the vimentin presented in the cell with a random network and capped around the nucleus. The results indicated that the cultured GHEF-III cells were fibroblast in origin. The cells were free of bacterial and mycoplasma contamination. The doubling time in GHEF-III was about 15 hours. Chromosomal analysis of GHEF-III presented a diploid stem cell line with a modal number of 44. No evidence of transformation of GHEF-III was shown by properties of contact inhibition, no colony formation in soft agar, and no tumor growth in nude mice. The transformation of GHEF-III after transfection with pT24-C3, an oncogenic plasmid, was shown by the evidence of loss of contact inhibition, growth in low serum medium, colony formation in soft agar and tumor growth in nude mice. In vitro transformation testing of these cells may provide valuable data in studying the role of tumor transforming genes in carcinogenesis. Owing to the genetic stability and less spontaneous transformation, this GHEF-III cell line can be utilized as a source of recipient cells in transfection assay.