Cell lines designated SNG-P and SNG-M were established from operation specimens of primary and metastatic regions of human endometrial adenocarcinoma. The cell lines grew well without interruption for over 13 months and were subcultivated more than 65 times. They continue to exhibit stable growth. The cultured cells appeared epithelial in shape, showing a pavement arrangement and multilayering without contact inhibition. The cytology revealed anaplastic and pleomorphic features. Upon electron microscopic observation, most of the cultured cells were characterized by highly indented nuclei with multiple large nucleoli and by desmosomal cell contact. The chromosomal number varied widely and showed aneuploidy, but the modal chromosomal number was stable at the diploid range. No marker chromosome could be identified. Both of these cell lines, SNG-P and SNG-M, were transplanted to an immune-depressed hamster cheek pouch and produced a tumor resembling the original.