1. Kinetic data for avian erythrocyte AMP-deaminase in lysate supernatants and 2000-fold purified enzyme were consistent with an allosteric model having four binding sites for substrate. 2. Relative to the purified enzyme, AMP-deaminase in lysate supernatants exhibited a greater S0.5 and enhanced sensitivity toward phytic acid, but was far less sensitive toward potassium ion. 3. In the absence of potassium chloride, the enzymatic activity in lysates exhibited hysteresis at subsaturating 5'-AMP. This response was modified reversibly by allosteric ligands. 4. It is concluded that the characteristics of avian RBC AMP-deaminase, as expressed in lysates, may reflect important intermolecular interactions and better represent the regulatory properties of this enzyme in erythrocytes.