- b Abstract Glycogen synthase kinase-3 (GSK-3) is a highly conservedserine ythreonine protein kinase that is involvedin the signal transduction cascades of multiple cellular processes. GSK-3 has two isoforms, designated a and b. GSK-3b protein levels andGSK-3 enzyme activity have been reportedto be red ucedby over 40% in postmortem frontal cortex of schizophrenic patients. GSK-3 is also present in peripheral tissue such as lymphocytes. In this study we aimedto findwhether the red uction in brain GSK-3 b measures is reflectedin peripheral tissue of schizophrenic patients. Fresh lymphocytes from schizophrenic patients showedno d ifference in GSK-3 a andGSK-3 b mRNA levels, GSK-3b protein levels, or total GSK-3 (aqb) enzyme activity comparedwith find ings in control subjects. In addition, lymphocyte-derived cell lines from schizophrenic patients did not differ in their GSK-3 b protein levels from levels in normal control subjects. The results rule out the use of lymphocyte GSK-3 as a marker for central GSK-3 abnormalities in schizophrenia. 2002 Elsevier Science Ireland Ltd. All rights reserved.