Evidence suggests that cannabinoid receptors, the pharmacologcial target of cannabis-derived drugs, and their accompanying system of endogenous activators may be dysfunctional in schizophrenia. To test this hypothesis, we examined whether endogenous cannabinoid concentrations in cerebrospinal fluid of schizophrenic patients are altered compared to nonschizophrenic controls. Endogenous cannabinoids were purified from cerebrospinal fluid of 10 patients with schizophrenia and 11 non-schizophrenic controls by high-performance liquid chromatography, and quantified by isotope dilution gas-chromatography/mass-spectrometry. Cerebrospinal concentrations of two endogenous cannabinoids (anandamide and palmitylethanolamide) were significantly higher in schizophrenic patients than non-schizophrenic controls (p < 0.05). By contrast, levels of 2-arachidonylglycerol, another endogenous cannabinoid lipid, were below detection in both groups. The findings did not seem attributable to gender, age or medication. Elevated anandamide and palmitylethanolamide levels in cerebrospinal fluid of schizophrenic patients may reflect an imbalance in endogenous cannabinoid signaling, which may contribute to the pathogenesis of schizophrenia.