The authors have studied the calcium content in the cerebrospinal fluid of 217 patients with miscelaneous neurological and psychiatric disorders; they have performed 244 determinations. They emphasize the importance in considering the two fractions of the total calcium. Since the diffusible fraction is the only one which has a definite significance, they studied all their material in order to find a simple way to determine it. They found a logarithmic relation between the protein and calcium contents and propose a formula by which would be possible to deduce the nondiffusible fraction [(0,91 χ log. protein content) - 1,3]. In cases of meningitis, brain and spinal tumors, hydrocephalus, neurosyphilis and cerebral hemorrhage, in which the spinal fluid presented a high content of both protein and calcium, they found that the diffusible calcium fraction was normal. Only in one condition, described by the french authors as the acute uremic psicotic encephalitis (Marchand's disease), they found a definite increase of the diffusible calcium content.