Human epidermal growth factor (gEGF), a potent stimulator of the growth of many tissues in culture, has been isolated from human urine and subsequently identified in many human biological fluids. We have partially purified and characterized hEGF-like substance(s) from human cerebrospinal fluid (CSF) and determined the concentrations of immunoreactive (IR) hEGF in CSF obtained from patients with a variety of neurological diseases. Competitive binding curves generated by the CSF samples appeared to be parallel to standard hEGF both in RIA and radioreceptor assays using human placental membrane. Sephadex G-50 gel exclusion chromatography of the CSF extract revealed a single peak of IR-hEGF which coeluted with standard hEGF. The apparent mol wt of the CSF hEGF-like substances(s) was estimated to be 8000 by sodium dodecyl sulfate poplyacrylamide gel electrophoresis, and its approximate pI was 4.5 as determined by isoelectric focusing. The concentrations of IR-hEGF in CSF from patients with pituitary and brain tumors and radiculomyelopathy were significantly higher than those from control subjects, while neither patients with hydrocephalus nor encephalomeningitis had CSF IR-hEGF levels statistically different from the control subjects. The presence of hEGF-like substance(s) in human CSF suggests that it may play an important physiological role in the function of the human nervous tissues but does not provide any evidence of its source.