The invention relates to novel [5,6-dichloro-3-oxo-9a-propyl-2,3,9,9a -tetrahydrofluoren-7-yl)]alkanoic acids and alkanimidamides, their derivatives and their salts. The compounds are useful for the treatment and prevention of injury to the brain and of edema due to head trauma, stroke (particularly ischemic), arrested breathing, cardiac arrest, Reye's syndrome, cerebral thrombosis, cerebral embolism, cerebral hemorrhage, cerebral tumors, encephalomyelitis, spinal cord injury, hydrocephalus, post-operative brain injury trauma, edema due to cerebral infections, various brain concussions and elevated intracranial pressure.