The last of four histamine receptors (HRs), H4 receptor (H4R), was identified in the year 2000. Since that time, the H4R has been implicated in cellular mechanisms related to immune systems, inflammatory processes, and allergic reactions. We have previously reported the expression of H4R mRNA in rheumatoid arthritic (RA) synovial cell cultures by means of the RT-PCR method. The present study demonstrates the expression of H4R at the protein level in RA synovial cell cultures. We also identified that the receptor was expressed in two specific types of cell populations, fibroblast-like and macrophage-like cells from RA synovial tissues. In the culture system, the fifth generation of fibroblast-like synoviocytes showed as strong expression of H4R as in the primary culture. The results provide pragmatic evidence for H4R as a novel target in the development of pharmacotherapeutic agents for RA treatment. Furthermore, the culture system used here will be useful for future studies concerning basic molecular mechanisms underlying the pharmacology of H4R.