The objective of this study was to examine the relationship between malondialdehyde-thiobarbituric acid (MDA-TBA) levels, as a measure of lipid peroxidation, in very low birthweight (VLBW) infants and outcome measures. A prospective observational longitudinal study was carried out in two level III neonatal units in the South Island of New Zealand measuring MDA-TBA levels in 61 VLBW infants in 1993. MDA-TBA levels were measured in (i) maternal plasma within 48 h of parturition, (ii) cord plasma, and (iii) infants' plasma at 2, 7, 14 and 28 days of age and correlated with antenatal and postnatal factors. Elevated levels of plasma MDA-TBA at 7 days were associated with adverse respiratory and ophthalmological outcome in the VLBW infants. Elevated MDA-TBA levels were measured at sample times close to the time of death in the infants who died. These results substantiate previously reported preliminary observations and support the hypothesis that oxidative injury, particularly within the first 7 days of life, is associated with the development of the long-term complications of the pre-term infant. MDA-TBA levels appear to be a useful measure to continue to explore the role of free radical mediated disease in the VLBW infant.