This report describes the recovery and characterization of neurotensin-like immunoreactivity (NT-LI) in human cerebrospinal fluid (hCSF). A large quantity of the fluid was fractionated by gel filtration, and subsequently separated and analysed by different high-performance liquid chromatography (HPLC) systems. The recovered material was analysed by microLC continuous-flow fast atom bombardment mass spectrometry, where a close similarity between one active CSF component and native neurotensin was confirmed. It was also found that, although a certain amount of the total NT-LI behaved as authentic neurotensin, the major part of the immunoreactive material was likely to be due to prestages and metabolites of the active peptide. The present finding is of importance for the development of efficient procedures for the quantitative analysis of neurotensin in hCSF samples.