Concentrations of somatostatin-like immunoreactivity (SLI) were examined in human cerebrospinal fluid (CSF). To validate the assay it was shown that CSF which had been run over a somatostatin immunoaffinity column showed no interference with binding of synthetic standards. Reversed phase HPLC showed that the immunoreactive material coeluted with SS14 and SS28 as well as a higher molecular weight precursor. Concentrations of human CSF SLI were stable at both room temperature and 4 degrees C for up to 72 h while repeated freezing and thawing resulted in a significant loss of immunoreactive material after the 3rd repetition. In normal control patients less than 55 years of age, CSF SLI was 54.7 +/- 1.9 pg/ml, while in those older than 55 CSF SLI was 56.2 +/- 2.2 pg/ml. Febrile infants had significantly higher levels (75.4 +/- 7.3) pg/ml. CSF SLI was normal in patients with aseptic meningitis (54.4 +/- 3.4 pg/ml), suggesting that increased CSF protein and white cell counts do not affect concentrations. Concentrations of CSF SLI were significantly increased in intervertebral disc disease (65.1 +/- 5.6 pg/ml), intrinsic spinal cord pathology (101.0 +/- 23.9 pg/ml), central nervous system tumors (78.0 +/- 7.8 pg/ml) and acute cortical damage of varied etiology (277.8 +/- 81.6 pg/ml). Patients with pseudotumor cerebri had concentrations of 43.2 +/- 2.5 pg/ml. Concentrations of CSF SLI were significantly reduced (P less than 0.01) in multiple sclerosis (38.8 +/- 5.5 pg/ml) and old cortical pathology (23.2 +/- 3.9 pg/ml). Serial CSF analysis in patients with acute CNS lesions, suggest that CSF SLI may be a neurochemical marker of acute pathology, as the initially elevated levels fell to or below normal with resolution of the pathologic process.