In collaboration with Prof Michio Matsuda of Japan, the study includes the clinical aspects, protein biochemistry and electron microscopical characteristics of an abnormal fibrinogen, which has been identified in a Pretoria family. By careful repetition of analysis of lysylendopeptidase digests of the gamma chain it was possible to identify an aminoacid substitution of Cys to Tyr at position gamma-139. By scanning electron microscopy, it would appear that the Pretoria fibrin fibers are significantly thinner than normal fibers with irregular aggregates scattered in the regular fibrin mesh