Objective: To determine the effects of magnesium sulfate (MgSO4) on tissue lactate and malondialdehyde (MDA) levels in rabbit brain after experimental head trauma. Design: Prospective, randomized trial. Subjects: Thirty New Zealand rabbits. Interventions: Group 1 (n = 10) was the sham operated group. Group 2 (n = 10) (untreated group) and group 3 (n = 10) received head trauma with the weight drop method. MgSO4 was administered 100 mg/kg (15%) i.v. immediately after the head trauma to group 3. Trauma was applied to one side. The non-contused side was named as "a" and the contused side as "b". Measurements: One hour after trauma, brain cortices were resected and the concentrations of lactate and MDA were determined using the spectrophotometric enzymatic and thiobarbituric acid methods. One-way ANOVA and Tukey's HSD tests were used for the evaluation of the results. P < 0.05 was considered as significant. Pearson's correlation test was used between lactate and MDA levels (P < 0.001). Results: There were significant differences between MDA and lactate levels of group 1 and all other groups; non-contused (a) and contused (b) sides of groups 2 and 3; groups 2b-3a, 2b-3b (P < 0.05). The difference in MDA levels was significant between groups 2a-3b (P < 0.05). Correlation between lactate and MDA was very good in group 1, and excellent in groups 2a, 2b, 3a, and 3b. Conclusions: These results demonstrate that head trauma leads to an increase in brain tissue lactate and MDA levels, and MgSO4 suppresses the rise in contused tissue when given after head trauma.