A complex investigation of the phenotype of a stable strain of LHC—162 cells derived from a spontaneous abortus was carried out. The karyotype, of the strain was 47,XY,+C. The extra chromosome was identified by Giemsa staining as a No. 7. The strain was subjected to cytomorphological, autoradiographic, immunochemical and virological examination in comparison with diploid cell strains. The cells of the LHC—162 strain had no oncogenic activity. Their susceptibility to the three types of poliomyelitis virus did not differ from those of diploid strains. The growth of the LHC—162 cells was poorly organized, and they had a reduced capacity for the formation of histotypical structures. There was low collagen production, poor accumulation of lipid granules, high acid phosphatase, activity, and high glycogen content. Radioautographic investigation of cell cycle revealed lengthening of the mitotic cycle in the G2, period which was twice as long as in diploid strains. Immunochemical investigation showed that fibroblasts of both trisomic and diploid strains synthesized proteins in α1 and α2 globulin zones. However, the synthesis of a protein in α1 zone was considerably more intensive and in α2 zone less intensive in the LHC—162 cells than in the diploid strain.