Using a specific radioimmunoassay we have measured somatostatin-like immunoreactivity (SLIR) of CSF in patients with brain atrophy, spinal spasticity, seizures, brain tumors and inflammatory disorders. Patients with marked brain atrophy had significantly decreased somatostatin levels in CSF. In patients with spinal spasticity significantly higher levels were observed. Seizure patients had reduced levels but the difference was not significant. In patients with inflammatory disorders and malignant brain tumors SLIR levels were significantly elevated but not in patients with benign brain tumors. A possible pathophysiologic meaning of SLIR in spasticity and seizures is discussed. The altered levels in brain atrophy, tumors and inflammatory disorders are probably indirect signs of altered somatostatin turnover or increased somatostatin leakage from damaged CNS.