Mouse brain adenosine deaminase was purified 1,240 fold. Potent adenosine deaminase inhibitors will be used in inhibition studies of the purified enzyme. Combinations of adenine arabinoside and adenosine deaminase inhibitors will be used to treat mice bearing CNS L1210. New potential periodate oxidation anticancer drugs will be synthesized, tested, and their mechanism of actions studied using flow microfluorometry and labeling experiments. The possibility of 2'-deoxycoformycin producing a chemically-induced severe combined immunodeficiency disease will be tested by several immunological methods.