Аннотация:The effect of two antitumour drugs, ftorafur (Ft) and 5-fluorouracil (5-FU) on chromosomes of human tumour cells (strain CA-1) was studied in vitro. Since no data on the karyotype of this tumour strain had been published, the chromosome set of the model was investigated at first. Significant quantitative and structural divergence from the normal human male karyotype were observed. Steam line cells contained 47-49 chromosomes, including 9 permanent markers. No Y-chromosome was revealed. Ft and 5-FU hardly injured the chromosomes of CA-1 cells; the level of aberrant metaphases reached 94%. Chromatid deletions and gaps formed the major part of drug-induced cytogenetic abnormalities.