Certain parameters were studied associated with lipid peroxidation (LPO) and antioxidant defense (AOD) in those newborn infants having been treated with the exogenous surfactant Alveofact (Boehringer Ingelheim, Germany). Kept under medical surveillance were 60 preterm infants presenting with primary pulmonary pathology and severe respiratory insufficiency aged 35 hours old. Of these, ten babies (the main group) received two dosages of the above drug, with the mean age at administration having been 17.36 +/- 6.54 hours. The time-related course was studied of the following parameters--lipid peroxidation potential (LPOP), non-enzymic antioxidant activity (AOA), blood serum content of lipid hydroperoxides, uric acid, bilirubin, iron, catalase and lactatedehydrogenase activities. Those babies having been given the surfactant demonstrated significantly lower LPOP basic level and higher non-enzymic AOA in the blood serum, which fact was related, in the first place, to a high incidence of grave forms of respiratory distress syndrome. The administration of two doses of the surfactant with a therapeutic purpose had no effect on subsequent systemic indices for LPO and AOD. It has been found out that high LPOP and low enzymic AOD in preterm infants presenting with grave primary affliction of the lungs can be one of reasons for development of surfactant-deficient states, and account for an inadequate clinical effect of exogenous surfactant drugs and for a poor prognosis.