To investigate regulation mechanisms of G2/M phase transition, we studied the association of cell cycle progression with p53-dependent p21/waf-1 and cyclinG expression. We used doxorubicin (DOX) and sodium butyrate (NaB) to accumulate p53 protein. DOX treatment resulted in an apparent increase of cells in the G2/M fraction, whereas NaB arrested cells at G1. P53 protein induction in response to DOX accompanied up-regulation of p21/waf-1 and cyclinG expression. However, cyclinG was undetectable in NaB-treated cells. These results implied a putative association between increases in the proportion of cells accumulating in the G2/M fraction and enhanced cyclinG expression. Antisense oligo DNAs (AS) complementary to cyclinG mRNA inhibited the cyclinG protein expression induced by DOX treatment. This inhibition resulted in a marked reduction in the number of cells arrested at G2/M and accumulating at G1. A role for cyclinG in G2/M phase transition control is implied.