Objective: All-trans-retinoic acid (ATRA) and interferons (IFNs) have been proven to synergistically amplify growth inhibition and apoptosis in the tongue squamous carcinoma cell line (Tca8113). Nucelar retinoic acid receptor-B (RAR B) was the key gene that mediated retinoid activity for squamous carcinoma cells. In order to understand the mechanism of ATRA combined with IFN y inhibiting growth of Tca8113 cells, this investigation focused on RAR B mRNA expression. Materials and Methods: In this experiment, RT-PCR method was used to analyze the RAR B expression level, and viable cell count assay was carried out for growth inhibition studies. Results: All-trans-retinoic acid (1 uM) and IFN y (1000 u/mL) inhibited cell growth by 39.2% and 44.4%, respectively. Synergistic inhibition of cell proliferation by 86.7% was found under combined treatment. The combination of suboptimal concentrations of ATRA (0.1 uM) with IFN y (1000 u/mL) showed a much stronger additive inhibitory effect on cell proliferation. ATRA (1 uM) and IFN y (1000 u/mL) increased RAR B expression to 4 times and 3 times, respectively. The expression of RAR B increased 12 times after treatment with combined ATRA and IFN y treatment. Conclusions: These observations indicated that the use of combined ATRA and IFN may lead to enhanced antitumor effects. These results also suggested that ATRA and IFN mediated upregulating expression of RAR B may play an important role in synergistic inhibition of proliferation in Tca8113 cells. (CJDR 1999;2(3)25-30)