Lipid emulsion (Intralipid) causes free radical-mediated damage to human cells in vitro. Incubation with 0.44% Intralipid for 17 h caused 40.3 +/- 3.8% haemolysis in adult human erythrocytes and 26.5 +/- 8.1% in erythrocytes from term newborns (p = 0.0001). In adult erythrocytes mean corpuscular volume increased 68.7 +/- 8.2% and in newborn erythrocytes 54.8 +/- 10.4% (p = 0.0012). Initial concentrations of reduced glutathione in adult and newborn erythrocytes were 65.1 +/- 2.5 and 62.1 +/- 4.0 mg/dl, respectively (ns); after incubation, glutathione concentrations were 21.0 +/- 4.0 and in 25.7 +/- 5.2 mg/dl in adult and newborn erythrocytes, respectively (p = 0.0004). After incubation the concentrations of thiobarbituric acid reactive material and conjugated dienes in newborn erythrocytes (2.8 +/- 0.2 microM and 0.223 +/- 0.019 OD 233, respectively) were higher than those of adult erythrocytes (2.1 +/- 0.4 microM and 0.138 +/- 0.012 OD 233) (p = 0.0001). In both adult and newborn erythrocytes, the effects of Intralipid were significantly inhibited by 0.6 mM deferroxamine or 8 mM sodium etidronate. Despite higher susceptibility to lipid peroxidation of the cell membrane, newborn erythrocytes are more resistant than adult erythrocytes to free radical-mediated effects such as depletion of intracellular glutathione, cell swelling and haemolysis.