Numerous personal and literary data on the karyotypic variation of cell lines during their establishing and long-term culturing have been reviewed. A new notion about karyotypic evolutionary pathways of cells in culture is presented. A detailed original approach to cytogenetic study of permanent cell lines is given, which allows, via karyotype reconstruction, to obtain finally a new karyotypic characteristics-the generalized reconstructed karyotype (GRK). Application of the cytogenetic approach as a criterion for the control of authenticity, purity and stability of cell lines is discussed. The cell line analysis by means of GRK elicited that the cell line evolution in vitro passes through two stages: a stage of establishment, and a stage of stabilization, both differing in karyotypic variability of cell populations and clonal selection in culture. The data indicate that it is important in experiments to utilize cell lines being in the stage of stabilization and to characterize chromosomally the cell line at the same passage when it is used. Above all, a comparison of karyotypic variations of tumor and leukemic cells in vitro and in vivo has revealed their common karyotypic evolution regularities (a nonrandom character of numerical and structural chromosome changes and the loss of one of the sex chromosomes) and the karyotypic evolutionary regularities characteristic solely of cells in culture. The main of these being a balanced chromosome set in the cell population as a whole and obligatory retention of diploidy in all chromosomes of the normal set by the majority of human and animal cell lines. It has been revealed that no less than two homologs of each autosome are present in cells of at least 85% of examined lines. Other cell lines (at least 15%) of a generally neurogenic origin are shown to be notable by keeping partial or complete monosomies on autosomes throughout the long-term culturing. Peculiarities of the karyotypic evolution of the latter are regarded in detail in addition to the data on the expression of oncogenes and other growth-associated genes in their cells. It is suggested that there are three main compensatory mechanisms through which cell lines with autosomal monosomies may maintain the vitality in culture: polyploidization of initial cell clones, oncogene amplification, mainly of the myc-family oncogenes, and fragmentary or complete extracopying of several autosomes. In summary, perspective of cell line cytogenetics as a field of biology of the cell in culture is discussed.