The results of the spectrophotometric analysis of 932 cerebrospinal fluid specimens are presented. The specimens were obtained from 95 patients with subarachnoid and intracerebral hemorrhages, 75 patients with traumatic head injuries, 40 patients with infectious diseases of the central nervous system, 302 patients with cerebrovascular accidents and 302 patients suffering from a variety of diseases such as multiple sclerosis, herniated intervertebral discs and vasomotor headache. Normal cerebrospinal fluid is colourless and shows a spectrophotometric absorption characterized by a flat curve with decreasing absorption from 350 to 650 nm. In disease states Oxy-Hemoglobin, Met-Hemoglobin and Bilirubin can be identified in cerebrospinal fluid. These pigments, when present in cerebrospinal fluid, change the spectrophotometric curve due to their specific absorption spectra. According to the quantitative relationship between the pigments and their chronological order of appearance in the cerebrospinal fluid, typical spectrophotometric patterns have been delineated. The spectrophotometric absorption curve of a hemorrhage due to rupture differs from that of a diapedetic hemorrhage. Moreover, tap bleeding results in an absorption curve which can be differentiated early from that of a subarachnoid hemorrhage. Finally, artifacts due to desinfectants can easily be identified. It is concluded that the spectrophotometric analysis of cerebrospinal fluid gives helpful information in subarachnoidal-hemorrhage, subdural and intracerebral hematoma, in contusions of the brain, carcinomatosis of the leptomeninx, spinal tumor and meningoencephalitis of unknown origin.