We studied the efficacy, pharmacokinetics, and brain entry of lorazepam in the treatment of status epilepticus (SE) using a rat model of secondarily generalized convulsive SE. Lorazepam entered the bloodstream rapidly following intraperitoneal injection. Brain concentrations peaked 10 minutes after peak serum levels were achieved. Lorazepam remained in brain longer than in serum, leading to increasing brain: serum ratios over time once peak serum levels had been reached. Free lorazepam was 9.1% of the total concentration in serum, a fraction similar to that which has been reported for humans. The median effective dose for control of generalized tonic-clonic seizures in this model was 0.94 mg/kg, which would produce a serum concentration of 196 ng/ml. Rats in SE had higher serum lorazepam concentrations than controls given the same doses, but lower brain: serum ratios, perhaps due to lactic acidosis during SE. Our data confirmed clinical reports of lorazepam's effectiveness as a treatment for SE and suggest that a target serum concentration of 200 ng/ml should be effective in most cases and provide seizure protection for 24 hours following treatment.