Abstract Residual fibrinogen remaining in a bovine plasma supernatant after precipitation of the majority of fibrinogen with 2.1 M glycine was isolated by a six-step procedure including two ethanol precipitations, two ammonium sulfate precipitations and a precipitation with β-alanine. The final purification was achieved by filtration over Bio-Gel A-5m. The material obtained had a clottability of about 80%. Gelelectrophoresis detected minor impurities, probably polymers, which remained soluble after coagulation of the monomers. The isolated material showed a prolonged thrombin time compared to stage I-4 fibrinogen and a decreased sedimentation constant s 20,w = 7.2±0.4 S. A molecular weight of 320.000±10% was determined by sedimentation equilibrium. A slightly lower molecular weight than stage I-4 fibrinogen was also estimated from the migration rate in gelfiltration. Following cleavage of disulfide bonds gelelectrophoresis as well as chromatography on CM-cellulose discerned γ-chains and a heavy β-fraction which, in addition to β-chains, probably included shortened α-chains indistinguishable from the β-chains by the methods employed.