40 patients (13 males, 27 females) with a mean age of 68 years presented organic brain syndromes of cerebrovascular etiology. They were studied to make an attempt upon the relationship between descriptive symptomatology on one hand and brain-blood-flow and oxidative metabolism on the other. The assessment of psychopathology and additional neurological and physical symptoms and signs was documented by the AMDP-rating scale system, then further computed by cluster analytic procedures. Cerebral blood flow (CBF) was measured by the Bernsmeier and Siemons (1955) modification of the Kety and Schmidt method. The cerebral metabolic rates of oxygen (CMR O2) and carbondioxide (CMR CO2) were determined by gaschromatography, the cerebral metabolic rates of glucose (CMR gluc) and lactate (CMR lac) by standard enzymatic methods. Five symptom-sign clusters were markedly differentiated by size and shape of their profiles. The mean values of the biological data within the clusters found did show different patterns of brain metabolism derangement with increasing tendency to reduced levels and functional decompensation. The latter reflected clinical deterioration in terms of psychopathology: disorders of cognitive functioning as well as psychomotor activity, social and illness behavior, i.e. need for special care. The cerebral metabolism balance worsened resulting in a widespread, gross disturbance of oxidative metabolism with a likely shift to anaerobic glycolysis. The lactate production was extremely heightened. CMR lac may be regarded as a causal quantitative factor significantly linked with pathogenesis, manifestation, and severity of organic brain syndromes.