The aim of this study was to assess the concentrations of selected components of the BBB: occludin, claudin-5, and zonulin (ZO-1), and to define a potential relationship between the concentrations of these three substances and the type of stroke, the location and extent of the infarct focus, the neurological/functional status in the acute phase of the disease, and the patient’s clinical profile. The gene discussed is CLDN5; the disease is Stroke.