Abstract.The parotid gland and knee joint of immunized rats were challenged with the sensitizing antigen. Sialoadenitis developed in over half of these rats after one and three challenges via the parotid duct. On the other hand, most glands were normal after five, seven and eight intraductal challenges in spite of the presence of precipitating antibodies in the scrum and hemagglutinating antibodies in the parotid saliva; in only a few animals did chronic destructive adenitis ensue. This contrasted with the incidence and severity of synovitis, which increased with the number of intra‐articular injections of antigen. The non‐reactivity of the gland is antigen specific in as much as acute adenitis resulted from intraductal instillation of a second antigen following multiple challenges with another one in rats sensitized with two antigens. The results evince a difference in the local reactivity between the salivary gland and synovial membr