A new cancer cell line (Lu-165) producing a large amount of anti-diuretic hormone (ADH, 2.8 micrograms/g protein) was established from a 50-year-old small cell lung cancer patient presenting with a syndrome of inappropriate anti-diuretic hormone secretion. These cells grew well in serum-supplemented medium and during more than 100 passages they continued producing a large amount of this hormone. This cell line will be a useful tool for studies of the biochemistry and pathology of ADH-producing cancer.