The paper describes a methodology for long-term cultivation of euploid cells from human and animal subjects, which overcomes the limitations of current tissue culture techniques. The authors have developed a method that uses pretested fetal calf serum and careful control of pH and temperature to minimize mitotic inhibitor action and maintain karyotype integrity. This technique allows for the reliable establishment of stable cell cultures from small skin biopsies, enabling genetic studies with individuals of known or suspected genetic markers. The cells, which are elongated and fibroblast-like, are nutritionally more demanding than epithelial-like cells but can be grown in media supplemented with fetal calf serum. The authors report successful cultivation of euploid cells from various human tissues and animals, including the Chinese hamster and American opossum, with minimal chromosomal abnormalities. The technique also allows for the isolation of clonal populations and the study of genetic changes in response to radiation and other mutagenic agents. The implications of these findings for genetic studies, diagnostic tools, and therapeutic applications are discussed.The paper describes a methodology for long-term cultivation of euploid cells from human and animal subjects, which overcomes the limitations of current tissue culture techniques. The authors have developed a method that uses pretested fetal calf serum and careful control of pH and temperature to minimize mitotic inhibitor action and maintain karyotype integrity. This technique allows for the reliable establishment of stable cell cultures from small skin biopsies, enabling genetic studies with individuals of known or suspected genetic markers. The cells, which are elongated and fibroblast-like, are nutritionally more demanding than epithelial-like cells but can be grown in media supplemented with fetal calf serum. The authors report successful cultivation of euploid cells from various human tissues and animals, including the Chinese hamster and American opossum, with minimal chromosomal abnormalities. The technique also allows for the isolation of clonal populations and the study of genetic changes in response to radiation and other mutagenic agents. The implications of these findings for genetic studies, diagnostic tools, and therapeutic applications are discussed.