The charge-heterogeneity of human plasma fibrinogen subunit chains was characterized by two-dimensional electrophoresis (2DE). Western blotting with antibodies specific for the gamma-chain demonstrated that the gamma-chains focus at varying isoelectric points (pI). This microheterogeneity was also observed in fibrinogen secreted from hepatocytic cells and in recombinant fibrinogen expressed in Chinese hamster ovary (CHO) cells. Further, covalent gammagamma-dimerization by FXIIIa was not influenced by the charge-heterogeneity, and removal of the carbohydrate did not reduce the number of gamma-chain pI variants. These observations suggest that the microheterogeneity of the gamma-chain is a multifactorial phenomenon that is not due to physiologic modification of the glycoprotein in circulation.