Abstract The effect of several tumor promoters (12- O-tetradecanoyl-phorbol-13-acetate (TPA); 1,1′-(2,2,2-trichloroethylidene)bis[4-chlorobenzene] (DDT); Aroclor1260, and clofibrate) on the inhibition of gap junctional intercellular communication (GJIC) and intracellular calcium concentration ([Ca 2+] i) was studied in a cell line consisting of initiated cells (3PC). In addition, the effect of different extracellular calcium concentrations ([Ca 2+] e) on the effects of tumor promoters on both GJIC and [Ca 2+] i were studied. Agents with GJIC inhibiting capacity increased [Ca 2+] i. However, the increase of [Ca 2+] i did not (always) precede GJIC inhibition. The effect of tumor promoters on GJIC were similar under low (0.05 mM) and high (1.20 mM) Ca 2+ e conditions, while different effects on [Ca 2+] i were found. These results suggest that tumor promoters can inhibit GJIC and change [Ca 2+] i, but that there is no direct relationship between these two processes.