AIM To determine NO, NO synthase (NOS) and NOSmRNA of the esophageal carcinoma cells (SHEEC1)in apoptotic process induced by As2O3 and to explore the relationship between NO and apoptosis.METHODS The apoptosis of the cell line (SHEEC1) was induced by arsenite (As2O3, 5 μmol/L and10 μmol/L). In the process, at 2 h, 4 h, 8 h, 16 h and 24 h after administration of As2O3, NO production incultural medium was detected quantitatively by spectrophotometry; NOS Ⅱ was detected byimmunohistochemistry and NOS mRNA by in situ hybridization (ISH). The cells at endpoint of theexperiment were examined under transmitted electron microscope (TEM) for apoptosis.RESULTS The amount of NO released from SHEEC1 were increased from the basal condition (0.68×10-2μmol/L) up to the high level (2.38×10-2μmol/L) at h 16. The increment of NOS Ⅱ was found afteradministration of As2O3; the intracytoplasmic ISH signals of NOSmRNA in small size was found firstly at4 h, and then became highly predominant. Apoptotic changes of SHEEC1 occurred at 24 h under TEM.CONCLUSION After administration of As2O3, NO released from cultured SHEEC1 cells was detected withincreasing amount up to 16 h. The expression of NOS H and transcription of NOSmRNA are upregulated.The present findings suggest a concept that the NO may be a mediated and effective factor in apoptosisinduced by As2O3,