The time dependence of N-acetyl-aspartate (NAA) concentrations relative to lactate and pyruvate in the injured rat spinal cord was investigated. Segments of spinal cord from regions rostral, caudal, and at the epicenter of the injury were analyzed. NAA concentrations were determined by gas chromatography-mass spectrometry and lactate and pyruvate concentrations were determined by UV spectroscopy at 20 min, 60 min, 2 h, 8 h, 24 h, 3 days, and 1 week after injury. NAA levels fell most significantly at the epicenter of the injury, reaching 30% of basal levels within 24 h. In all segments, lactate levels increased significantly shortly after injury, peaking at two to five times normal basal levels between 20 and 60 min after injury. Rostral and caudal to the injury site, lactate elevations and NAA reductions were less dramatic. Pyruvate concentrations were not significantly altered in any of the sections after injury. The temporal and spatial relationships of NAA and lactate changes indicated that ischemic conditions due to injury in the upper thoracic rat spinal cord were distributed asymmetrically. Acute ischemia was more severely caudal to the injury site, and NAA concentrations were more severely impaired in the rostral direction. The results suggest that the extent of neuronal degeneration due to spinal cord injury does not correlate directly with acute ischemic severity as measured by the lactate/pyruvate ratio, and may be more closely related to secondary changes in the neuronal environment.