The human kallikrein gene family consists of 15 serine proteases. We examined the expression of the kallikrein genes in human cerebral cortex and hippocampus by RT-PCR and compared their expression between Alzheimer's disease (AD) and control tissue. KLK1, 4, 5, 6, 7, 8, 10, 11, 13 and 14 are expressed in both cerebral cortex and hippocampus. KLK9 is expressed in cortex but not hippocampus, whereas KLK2, 3, 12 and 15 are not expressed in either tissue. We demonstrate an 11.5-fold increase in KLK8 mRNA levels in AD hippocampus compared to controls. The KLK8 gene product, neuropsin, processes extracellular matrix and is important for neuronal plasticity. Therefore, the increase in KLK8 could have detrimental effects on hippocampal function in AD.