To the Editor:— Adenine in the form of the free base alone or mixed with monobasic sodium phosphate was given orally in daily doses ranging from 300 to 500 mg. each to 5 dogs over a period of one to three weeks. The dogs were kept on a normal diet (K. F. S. [Kennel Food Supply] dog food). After ten to twenty days of treatment all these dogs developed multiple avitaminosis (blacktongue) and a rise in blood pressure. The addition of the phosphate accelerated the onset and development of the syndrome. These findings are of interest to the physician since they demonstrate a direct relationship between purine metabolism and avitaminosis and suggest caution in the use of adenine as a therapeutic agent.