A new dipeptide was isolated from several tissues of Agkistroden blomhoffi (mamushi: a venomous snake in Japan), using ion-exchange resins and thin-layer chromatography. It was identified as O-phosphoserylethanolamine by mass spectrometry and comparison with synthetic compounds using several methods. This compound was contained in several mamushi tissues including the liver, heart, brain, bile, and muscle. The concentrations of O-phosphoserylethanolamine in the liver, brain, muscle, skin, heart, and bile were 7.17 +/- 3.11, 16.98 +/- 4.25, 37.37 +/- 7.88, 37.56 +/- 8.97, 23.93 +/- 6.11, and 22.21 +/- 5.76 mumol/g, respectively. (C) 2002 Elsevier Science (USA). All rights reserved.