The efficiency of the binding of RNase 7P molecules to albumin on cocondensation with the aim of producing the prolonged action forms of the enzyme can be increased by using ligand-free human serum albumin (LFHSA). The CD method showed that LFHSA underwent changes of the cooperative character under the action of acid and urea. On potentiometric titration the number of titrated groups of LFHSA decreased with time. The GPC method demonstrated the RNase bound more efficiently to freshly dissolved LFHSA. In this case part of the enzymic activity was manifested only after proteolysis of the albumin carrier. Cocondensation with the aid of glutaraldehyde resulted in the formation of LFHSA-RNase conjugates composed of 1-2 moles of human serum albumin and 1-6 moles of RNase. More than 50% of transferase activity retained in the blood plasma for 2-3 days after intravenous injection of the conjugates with a molecular weight of 70-80 kD to rabbits.