Fourteen patients with essential mixed cryoglobulinemia were studied. The relevance of fibronectin (FN) in cryoprecipitation seems to be of relative importance since only two thirds of the cryoprecipitates have a higher cryocrit level when FN is present. On the other hand, the other samples show a lower precipitating activity after plasma heating at 60 degrees C. This reduction may reflect either a structural FN modification by heating or the denaturation of other cryoprecipitating molecules. It is possible, even if not necessary, that at least in vitro FN plays a role in the cryoprecipitate formation.