Clinical reports are published for only two patients with homozygously expressed congenital dysfibrinogenemia. The patients, both of whom have a bleeding diathesis, have amino acid substitutions in the fibrinogen molecule at A alpha 16 Arg----Cys and A alpha 19 Arg----Ser, respectively. We report that a third patient with dysfibrinogenemia (fibrinogen Giessen I) is homozygous for A alpha 16 Arg----His. Although this patient has had excessive postpartum bleeding, she has had normal hemostasis throughout several minor surgical procedures and hysterectomy. Elucidation of the amino acid alterations in patients with dysfibrinogenemia may expand our understanding of structural determinants of fibrinogen that are critical to its function in vivo.