Heterochromatin of chromosomes is studied by means of a C-banding technique for the J-96 line of human cells, which is susceptible to enteroviruses and for the J-41 cell line derived from this culture and possessing high specific resistance to Coxsackie B viruses. The data obtained demonstrate stability of variform C-heterochromatin of chromosome pairs 1, 9 16 and certain marker chromosomes in the course of long-term cultivation.