Amyloid deposition in the articular structures occurred with high frequency in a strain of mice now being established as an animal model of senescence in this laboratory. The changes were most evident in the knee joint. Peripheral joints were always spared. The lesions appeared after 7 months of age, and the incidence reached 88% (7 of 8) in autopsied mice over 8 months of age. This is the first report of amyloid deposition in the joints of laboratory animals.