Purification of annexin IV and VI from porcine liver was achieved by Mono Q ion exchange chromatography at pH 8.9 and pH 7.5, respectively. The isolated proteins interacted with erythrocyte membrane as function of calcium ion and the protein concentration. Half-maximal binding of annexin VI to erythrocyte membrane was found to occur at 8 microM Ca2+. The maximal binding was estimated as 2 micrograms of annexin VI per 1 microgram or erythrocyte membrane protein, in the presence of 100 microM Ca2+. The property of erythrocyte membrane to interact with annexins was utilized in preparation of a affinity-column with polyacrylamide-immobilized erythrocyte membrane.