2'-adenosine diphosphate and 3'-adenosine diphosphate were made from the corresponding unprotected nucleoside monophosphates using phosphoramidic acid. This synthesis of the pyrophosphate link was stimulated by pyridine. Both compounds were more labile than 5'-ADP, and they were shown to degrade by two separate routes. The degradation rate determining path seems to be cyclization with the vicinal hydroxyl, to form 2', 3'-cyclic AMP. A direct cleavage of the pyrophosphate link is an alternate slower route. Degradation curves at pH 3.5, 7.0 and in 7N ammonium hydroxide, at 100° C, are given. 3'-ADP was shown to be less stable than 2'-ADP at acid and neutral pH's, probably due to an increased nucleophilicity of the 2'-hydroxyl resulting from hydrogen bridging to the nitrogen in the 3 position of adenosine. Both compounds were found to be remarkably stable in 7N ammonium hydroxide at room temperature. The action of various enzymes was tested on these materials.. Bacterial alkaline phosphomonoesterase was active on both. Ribonuclease T₂ was active only on 3'-ADP and produced 3'-AMP. Snake venom diesterase and spleen diesterase were inactive on both.