When human Bel-7402 hepatocarcinoma cell line grew in a medium containing 10 - 4 M dimethyl-4,4 -dimethoxy-5,6,5 ,6 -dimethylenedioxybiphynyl-2,2 -dicarbox ylate (DDB), the secretion of α-fetoprotein (AFP) was significantly lower than the control cells, whereas the albumin (ALB) secretion was markedly higher. The activity of γ-glutamultranspepeidase (γ-GT) in DDB-treated cells markedly decreased in comparison with the control cells. On the contrary, the activity of tyrosine-α-ketoglutarate transaminase (TAT) was higher in DDB-treated cells than in control cells. DDB (10 - 4 M) could significantly increase the content of cAMP in Bel-7402 cells, and also enhance the expression of anti-oncogene p53. The results suggest that DDB has reversing effects on the phenotypes of the human Bel-7402 hepatocarcinoma cell line.