Prior studies show that in ASIC3-/- mice mechanical hyperalgesia does not develop in animals with either an inflammatory or a non-inflammatory muscle injury; however mechanical hyperalgesia still develops after cutaneous inflammation. We tested if mechanical hyperalgesia develops in ASIC3-/- mice with joint inflammation, and if ASIC3 is present in primary afferent fibers innervating the joint. After inflammation of the knee joint, there is an increase in the number of responses to mechanical stimuli in ASIC3+/+ mice. This increase in mechanical sensitivity does not occur in ASIC3-/- mice with joint inflammation. Immunohistochemical analysis of the knee joint capsule from ASIC3+/+ (non-inflamed) failed to localize ASIC3 to primary afferents as noted by lack of neuronal co-localization (PGP9.5). ASIC3 was found, however, in the synovial lining where it co-localized with hyaluronic acid (HA) and the type B synoviocyte marker Hsp25. The synovial lining of ASIC3-/- mice were void of ASIC3. Although unexpected, the presence of ASIC3 in type B synoviocytes is in accordance with reports that the synthesis of the joint lubricant HA increases in vivo due to synovial lining stress and is regulated in isolated type B synoviocytes in a mechanosensitive manor. ASIC3 plays a role in mechanical hyperalgesia associated with joint inflammation. The co-localization of ASIC3 with HA and type B synoviocytes supports the hypothesis that ASIC3 is also involved in modulating the secretion of HA from synoviocytes. At present, the precise role of ASIC3 on Type B synoviocytes is unknown but suggests ion channels modulate both sensory neuron transmission and non-neuronal cell activity. Supported by AR053509.