V79-8 is an abnormal cell line which does not have detectable G1 and G2 phases in its cell cycle. This cell line is derived from V79 cell line which has G1 phase but lacks G2 phase. By using an anti-sense approach, CDK4 gene expression was partially inhibited to find whether CDK4 might contribute to the lack of G1 phase in V79-8 cells. Anti-CDK4 anti-sense plasmid was constructed and used to transfect V79-8 cells. Clones of transfected cells (V79-8-asCDK4) were examined, in comparison with V79-8 cells. to determine its growth curve, cell doubling-time (GT), the level of CDK4 gene expression and the levels of expression of some other growth related genes. V79-8-asCDK4 cells showed a slower growth rate with a doubling time 2.5-h longer than that of V79-8 cells. A flow cytometry (FCM) analysis demonstrated that the 2.5h increse of the doubling time of V79-8-asCDK4 cells was mainly due to the appearance of G1 phase because its G2+ M phase was not significantly different from that of V79-8 cells. The decrease of CDK4 gene expression in V79-8-asCDK4 cells was shown by Northern-blot. Changes in the expression levels of the growth-related genes TGF-