antibodies against crystals we suggest that crystals when introduced into an organism may behave as conventional antigens mediating the production of specific antibodies these antibodies would bear an imprint of the crystal surface and may consequently behave as a nucleating matrix in a new crystallization event thus they would behave as catalytic antibodies we show that igg antibodies isolated from patients suffering from gout a joint disease caused by crystals of monosodium urate monohydrate msum accelerate the appearance of new crystals of msum from a supersaturated solution of the salt in vitro the same effect is not observed for igg antibodies isolated from the joint fluids of patients with other joint diseases such as pseudogout rheumatoid arthritis or osteoarthritis furthermore igg antibodies obtained from rabbits injected subcutaneously with crystals of msum were also nucleating towards msum crystals