Lysates of human erythrocytes produce pain when applied to a human blister base. The algogenic material is not potassium, acetylcholine, bradykinin, 5-hydroxytryptamine, histamine or a prostaglandin, and is dialysable. 2. Fractionation of dialysates of freshly lysed erythrocytes by Sephadex gel filtration coupled with assays on the human blister base preparation showed that the algogenic material was a mixture of the adenyl compounds adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP). 3. On the human blister base preparation ATP, ADP and AMP had comparable activity and produced threshold pain in a concentration of 2 muM. 4. The rabbit isolated jejunum preparation was found useful in these studies since ATP, ADP and AMP produced a relaxation which was proportional to their concentration in test samples obtained from dialysates. Of more limited usefulness was the rat isolated stomach strip preparation on which ATP and ADP produced contractions which also were proportional to their concentrations in text samples. 5. The possible role of adenyl compounds in the production of pain in vivo is discussed.