Proliferation of esophageal cancer cells stably transfected with regenerating gene (REG) I was measured as a function of WST‐8 cleavage (a). Cell viability was assessed using MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyltetrazolium bromide) assays. Cells were treated with radiation at dose of 5 Gy or 10 Gy (b), with 0.1, 1.0, 5.0, or 10 µM cisplatin (c), or with a combination of 5 Gy radiation and 0.1, 1.0, 5.0, or 10 µM cisplatin (d). REG I transfectants were significantly more susceptible to chemo‐, radio‐ and chemoradiotherapy than control cells. All results are expressed as the means ± SD of 10 samples; *P < 0.01.