Enterostatins belong to a family of peptides (e.g., Val-Pro-Asp-Pro-Arg, VPDPR; Ala-Pro-Gly-Pro-Arg, APGPR; and Val-Pro-Gly-Pro-Arg, VPGPR) derived from the tryptic cleavage of amino-terminal pentapeptide from procolipase. Pharmacologic studies have suggested a role for these peptides in appetite regulation and insulin secretion. Studies into the distribution of enterostatins or the role of endogenous peptides have not been possible until now due to the lack of a suitable method for assay. Using two polyclonal antibodies raised against VPDPR and APGPR and different chromatographic methods, we have examined the nature and distribution of enterostatin-like immunoreactivity in human cerebrospinal fluid. The results reported here show for the first time the presence of enterostatin-like immunoreactivity in the human cerebrospinal fluid. Further characterization of cerebrospinal fluid enterostatin-like immunoreactivity revealed that it is not due to APGPR, VPGPR, or VPDPR but to another peptide similar to VPDPR.