Abstract: A pharmaceutical composition is prepared wherein a biologically active conjugated protein is selectively conjugated to at least one heparin fragment having a terminal 2,5-anhydro-D-mannose residue which has an aldehyde not involved in intramolecular hemiacetal formation. The resulting conjugate has a prolonged half-life as compared to native protein and is able to deliver heparin to the site of clots or to prevent reocclusion within the blood stream. Typical proteins include enzymes such as plasminogen activators, and in particular tissue plasminogen activators, and erythropoietin, hormones, antibodies and the like.