We examined normal and abnormal fibrinogen (fibrinogen "Grenoble") by two-dimensional gel electrophoresis to obtain data on possible defects at the molecular level. Fibrinogen Grenoble is characterized by an abnormal rate of fibrin monomer aggregation. The electrophoretic analysis revealed the presence of abnormal gamma chains. Two kinds of gamma chains can be detected in fibrinogen Grenoble: (a) normal gamma chains and (b) gamma chains Grenoble (gamma G) with a greater molecular mass but no modification in isoelectric point. The latter chain can be detected in whole plasma by two-dimensional gel electrophoresis. Metrological analysis was performed in an attempt to quantify observed differences between normal fibrinogen and fibrinogen Grenoble. On use of gels stained either with Coomassie Brilliant Blue or with silver, the partly qualified evaluation gives about 60% normal gamma chain and 40% gamma chain Grenoble.