The inducible c-myc antisense RNA expression plasmid PGXC expressed in mammalian cells was constructed. PGXC was cotransferred with plasmid pSV2neo which confers resistance to Geneticin (G418) to human promyclocytic leukemia cell line HL60. Following the promotion of c-myc antisense RNA expression with Cd~(2+) the growth rate of transfectant HL_(60)~R-9 was significantly slower than that of the parent cells HL60. Flow cytometric analysis indicated a marked increase in Gl fraction and decrease in S-phase population in the cell cycle of transfectants. The differentiation of cellular morphology and function of HL_(60)~R-9 was induced. HL_(60)~R-9 did not form colonies on soft agar and had reduced or lost the tumorigenicity in nude mice.