Although the pathogenesis of schizophrenia is unknown, there are data which indicate that the disease may be due to neurodevelopmental disturbances. Cell recognition molecules such as N-CAM and L1 antigen are involved in cell-cell interactions during development and in plasticity of the nervous system and could therefore be altered in relation to ongoing or established pathological processes. Using the Western blot technique, we found significant increases in N-CAM immunoreactive proteins and decreases in L1 antigen in the CSF of schizophrenic patients as compared to normal controls. The decrease in L1 antigen was observed in the 140-kDa band, and N-CAM was increased only in the 120-kDa band. The 120-kDa band of N-CAM and the 140-kDa band of L1 antigen were prominent components of CSF, but in serum these bands were minor or not detectable. Neuroleptic treatment did not significantly change either N-CAM or L1 antigen concentrations in CSF. It is possible that these CSF proteins are derived from CNS cells as secreted soluble N-CAM isoforms and L1 peptides. Our results suggest the possibility of a specific pattern of abnormal cellular function in the CNS in schizophrenia. (C) 1995 Academic Press, Inc.