Histidine decarboxylase catalyses the formation of histamine, an important biological messenger. In spite of the essential biological functions exerted by histamine the knowledge about the mechanisms involved in the regulation of histidine decarboxylase is rather limited. This is most likely due to the limited supply of suitable tools, including highly specific antibodies. In the present study we describe the production and characterisation of specific antisera against rat histidine decarboxylase using recombinant protein synthesised in a bacterial expression system. The antisera were shown to effectively immunoprecipitate histidine decarboxylase activity in extracts of fetal rat liver as well as to detect the histidine decarboxylase protein by Western blot analysis of COS-7 cells expressing recombinant rat histidine decarboxylase. The results demonstrate the successful production of highly specific antisera to histidine decarboxylase which may become valuable tools in future studies of the structure and function of this enzyme.