Plasma magnesium, calcium, and oxidative status were investigated in 31 male casualties with traumatic brain injury (TBI) during a 7-day posttraumatic period. The study group consisted of eight patients with mild closed head injury (Glasgow Coma Scale score [GCS] of 13-15), 10 patients with extensive penetrating head injury (GCS 4-6), and 13 patients with blast injuries but without direct head trauma. The latter group was included since previous experimental and clinical data have confirmed the development of indirect brain trauma in patients with blast injuries. Patients with multiple injuries were not included. Significant declines in plasma divalent cations were found in GCS 4-6 patients immediately after TBI and persisting for the entire 7-day study period. Similar changes in magnesium, but not calcium, were present in the GCS 13-15 and the blast injury groups, but only up until day 3 after injury. Alterations in lipid peroxidation products and superoxide anions were also observed following TBI. Increased lipid peroxidation was noted in all three groups over the entire posttraumatic period while increases in superoxide anion generation occurred transiently immediately following TBI. Thereafter, in the GCS 13-15 and blast injury groups, superoxide anions subsequently normalized, whereas in extensive head injury (GCS 4-6), superoxide anion generation significantly declined. A negative correlation between magnesium balance and oxidative stress was observed in all patients immediately after injury persisting in GCS 4-6 patients to the end of the observation period. Our findings suggest an interrelationship between magnesium changes and blood oxidants/antioxidants after TBI, which could be of both diagnostic and prognostic value in patients with neurotrauma.