A solid-phase enzyme immunoassay of human lactoferrin wus developed, which was used in diagnosis of some septic diseases. The test system developed enabled lactoferrin to be measured in the blood serum and plasma of healthy volunteers: 955.8 +/- 74.4 and 405.5 +/- 27.7 mg/e, respectively. This assay may be used also in measurement of blood serum lactoferrin levels in various pathological states and particularly applied for detection of postnatal pyoseptic failures before their clinical manifestations.