This study concerns a patient with the association of cryoblobulinaemia and cold urticaria. The cryoglobulin was exclusively kappa type IgG. The cold urticaria was passively transferred to normal recipients utilizing the isolated cold precipitable IgG and the cryoprotein-containing whole serum. In vivo mast cell degranulation was associated with the induction of the cold urticaria in the patient and in vitro basophil degranulation was induced by the isolated cryoprecipitate. Therefore, the interrelationships between the cold stimulus, cryoprecipitation, mast cell degranulation, histamine release and cold urticaria has been established.