An investigation was made in the cerebrospinal fluid of 82 patients who had bleeding into the subarachnoid space or other neurologic disorders in order to study the macrophages. The ages of these patients ranged from 24 hours to 80 years. It was verified that the macrophages with red blood cell could be demonstrated from 24 hours until 30 days after the onset of the bleeding. The macrophages with hemosiderin were observed after the 6th day after the onset of the bleeding, and they could be seen in some cases after 70 days. It was discussed the assertion that the simultaneous presence of red blood cell and hemosiderin in the cytoplasm always indicates repeated hemorrhages. In a 24-hour-old newborn baby with bleeding in the subarachnoid space it was found macrophage with hemosiderin. This anomalous finding pointed out to hemorrhage during the intrauterine life.