Immunoenzymatic assay (IEA) was used to study the content of fibrinogen and its splitting products (FSP) in patients with pyelonephritis and glomerulonephritis. The active phase of the disease was characterized by a marked increase of the fibrinogen content and FSP in the blood. The changes reflect the process of activation of the blood coagulation system with hypercoagulation phenomena. Immunoenzymatic assay is perspective for the evaluation of the state of hemostasis in renal diseases and for controlling treatment efficacy.