The present work has endeavored to survey the occurence of adenosine deaminase as well as its multiple forms in normal and some cancerous human tissues. A recent report by Akedo, Nishihara, Shinkai and Komatsu concerning the appearance of the C form adenosine deaminase in cancerous tissues is investigated. The thesis reports, however, the occurence of both A and C forms of adenosine deaminase in almost all normal and cancerous tissues investigated. An increase in C form adenosine deaminase does seem to occur in cancerous tissues, and a ratio method is developed to monitor such an increase in the C form enzyme.Fundamental catalytic and physical parameters are used to characterize the A and C forms of adenosine deaminase in several normal human tissues. Little difference is noted between the two forms of the enzyme. Only substrate specificity for cordycepin is of significant value in differentiating between the A and C forms of the enzyme.