Acute osmolar loading of cerebrospinal fluid within one lateral ventricle of dogs was examined as a cause of water extraction from the bloodstream and an increase in intracranial pressure. We have shown that a certain amount of 3H2O from the bloodstream enters osmotically loaded cerebrospinal fluid significantly faster, hence causing a significant increase in intracranial pressure. The noted phenomenon in which intracranial pressure still significantly increases, but in which the hyperosmolarity of the cerebrospinal fluid is no longer present, was named "compensated hyperosmolarity". In the case of the sub-chronic application of hyperosmolar solutions into cat ventricles, we observed an increase in cerebrospinal fluid volume and a more pronounced development of hydrocephalus in the area of application, but without significant increase in intracranial pressure and without blockage of cerebrospinal fluid pathways. These results support the newly proposed hypothesis of cerebrospinal fluid hydrodynamics and the ability to develop new strategies for the treatment of cerebrospinal fluid-related diseases. ----- KEYWORDS: CM, CP, CSF, HRP, ICP, ISF, LLV, RLV, SAS, SD, cerebrospinal fluid, cerebrospinal fluid hydrodynamics, cerebrospinal fluid hyperosmolarity, choroid plexus, cisterna magna, horseradish peroxidase, hydrocephalus, interstitial fluid, intracranial pressure, left lateral ventricle, right lateral ventricle, standard deviation, subarachnoid space