It is known that the tissue level of adenine nucleotides changes when the whole animal is treated with certain drugs or X-ray irradiation. Mor (1) has observed a decrease of adenosine triphosphate (ATP) and an increase of adenosine diphosphate (ADP) in the liver and skeletal muscle of the guinea pigs treated with fever-producing substances such as dinitrophenol and bacterial lipopolysaccharide. He has also obtained a similar result in the animals anaesthetized with magnesium sulfate. Kirpekar and Lewis (2, 3) and Kaul and Lewis (4) demonstrated that reserpine causes a simultaneous fall in the levels of ATP and catecholamines in the rat adrenal medulla and brain. It is also reported that X-ray irradiation brings about a significant decrease in the 32P incorporation to the phosphorylated nucleotides of the spleen and thymus in mice transplanted with mammary carcinoma and that these changes may result from an inhibition of the phosphorylation in the irradiated tissue (5, 6). Evidences have been accumulated for the past decade suggesting that the formation and utilization of ATP are involved in the mechanism of histamine release during anaphylactic reaction. It was reported from several laboratories, that the histamine release in vitro is potentiated on the addition of succinic acid (7, 8) or glucose (9), and is inhibited by respiratory inhibitors such as malonate, cyanide and anoxia (7, 8, 10), and by uncouplers of oxidative phosphorylation such as dinitrophenol (8, 10, 11). However, it still remains unclarified just how the level of adenine nucleotides would change in the shocked organ during anaphylactic reaction. The present paper describes the results of an investigation on the adenine nucleotide contents of the liver and 'lung of guinea pigs, as determined by the ion exchange chromatographic method. The determination was made in normal as well as in the sensitized guinea pigs injected with antigen.