Subarachnoid hemorrhage (SAH) develops when extravasated arterial blood enters subarachnoid space and mixes with cerebrospinal fluid. As a result, many pathologies develop, including increase in brain-blood barrier (BBB) permeability and activation of peripheral leukocytes, that in turn augment immuno-inflammatory response, considered as the cause of numerous complications following SAH. In the study, we examined the role of one of the major cytokines, interleukin 1-beta (IL-1beta), in the BBB rupture and subsequent migration of leukocytes into central nervous system (CNS) after experimental SAH in adult rats. SAH was produced by injection of 150 uL of autologous arterial blood into cisterna magna. In 50% of animals, IL-1beta activity was inhibited by intracerebroventricular administration of anti-rat IL-1beta antibodies (SAH groups). Control group consisted of sham-operated rats. Ninety minutes or 24 hrs following surgery, blood samples were taken, then animals were perfused transcardially and whole brains were collected. Three major populations of leukocytes present at brain stem and frontal part of the brain – granulocytes, monocytes/macrophages and lymphocytes – were labeled with appropriate antibodies. S-100B protein concentration in the serum, a marker of BBB permeability, was also measured. Neutralization of IL-1beta activity reduced elevated S-100B level and the number of leukocytes found within the CNS, however these changes were not uniformly significant among different subgroups. The results demonstrate an important role of IL-1beta in the BBB damage and leukocyte migration into the CNS subarachnoid hemorrhage.