The PCD17 protein is a paraneoplastic cerebellar degeneration (PCD)-associated neural autoantigen which is recognized by autoantibodies in sera of PCD patients. The localization of the PCD17 mRNA was examined by in situ hybridization histochemistry using a PCD17 cRNA probe. In the cerebellum, the localization of the transcript was in agreement with the distribution of PCD17-immunoreactivity. On the other hand, intense hybridization signals were detected in most of cells in the hippocampus in which notable PCD17-immunoreactivity was undetected. These observations suggest that some negative translational or post-transcriptional mechanisms of the PCD17 mRNA may be involved in neurons of the hippocampus.