A reactive synovitis secondary to intra-articular particles of silicone elastomer developed in three patients who had undergone Silastic hemiarthroplasty. In an attempt to duplicate this phenomenon, we used an animal model in which finely ground particulate silicone elastomer was introduced into the knee joints of adult New Zealand White rabbits. In three of thirteen rabbits (p = 0.066) histological evidence of inflammatory changes developed in the synovial tissue, similar to those seen in our patients. Intraarticular particulate silicone elastomer created by abrasion of a Silastic hemiarthroplasty may be responsible for the development of an iatrogenic reactive synovitis.