Damage to white matter in some premature infants exposed to intrauterine infections is thought to involve disruption of the blood-brain barrier. We have examined the effect of minocycline, an agent reported to reduce brain damage resulting from inflammation, on inflammation-induced disruption of the blood-brain barrier and damage to white matter. Post-natal marsupial opossums (Monodelphis domestica) were studied as most brain development in this species occurs after birth. Single intraperitoneal lipopolysaccharide (LPS) injection (0.2 mg/kg) with or without minocycline (45 mg/kg) at post-natal day (P)35 caused short-lasting barrier breakdown to plasma proteins but not to (14)C-sucrose. By P44, blood-brain barrier integrity was intact but a reduced volume of white matter was present. At P44 after prolonged inflammation (5 x 0.2 mg/kg LPS at 48 h intervals), proteins from blood were observed within brain white matter and permeability to (14)C-sucrose in the hindbrain increased by 31%. The volume of the external capsule and the proportion of myelin were 70 and 57%, respectively, of those in control animals. Minocycline administered during prolonged inflammation restored blood-brain barrier integrity but not LPS-induced damage to white matter. These data suggest that long-term changes in blood-brain barrier permeability occur only after a prolonged period of inflammation during development; however, damage to white matter can result from even a short-lasting breakdown of the barrier. Manipulation of the inflammatory response may have implications for prevention of some developmentally induced neurological conditions.