Background: Preeclampsia is a disorder characterized by high blood pressure and often proteinuria during pregnancy. It is known that a subseptic dose of bacterial lipopolysaccharide (LPS) induces production of proinflammatory cytokines, and possibly increasing the risk for developing preeclampsia. We investigated the effects of LPS on the blood-brain barrier (BBB) integrity in pregnant rats with N (omega)-nitro-L-arginine methyl ester (L-NAME) induced preeclampsia. Methods: Starting from the 10th day of gestation, pregnant rats were given L-NAME for 10 days to produce hypertension and proteinuria. Animals were then treated with a single injection of LPS on the 19th day of pregnancy. Arterial blood pressure and proteinuria were measured on the day of the experiment, which was 24 hours after the LPS injection. The BBB integrity was assessed by using Evans blue (EB) and horseradish peroxidase (HRP) tracers. Results: Proteinuria was observed in varying degrees, and the arterial blood pressure increased in L-NAME-treated pregnant rats (P < .01). The overall brain EB content did not increase in these preeclamptic rats when compared to pregnant animals, and LPS treatment also did not change EB content. Ultrastructurally, frequent vesicles containing HRP reaction products were observed in the capillary endothelial cells in the cerebral cortex and hippocampus of pregnant rats treated with L-NAME (P < .01). However, LPS did not change the amounts of HRP that mainly accumulated in brain capillary endothelial cells of these animals. Conclusion: Our results suggest that, in this experimental setting, LPS does not change the severity of BBB disruption observed in preeclamptic animals.