Cryoglobulins are proteins or protein complexes that undergo reversible precipitaton at low temperatures. Their classification includes monoclonal, mixed monoclonal-polyclonal and mixed polyclonal cryoglobulins. The mechanism of cryoprecipitation remains still unanswered and the incidence of mixed cryoglobulinemia in patients with chronic HCV infection has only little evidence. However, mixed cryoglobulinemia could represent a crossroad between a classic autoimmune disorder and malignancy. In order to realise an adequate characterisation, cryoglobulins are cooled below core body temperature, than repeatedly washed to remove nonspecifically adherent serum proteins and other blood elements. After such a process the cryoglobulins are resolubled by warming to 370C and only then analyzed. Because the testing for cryo-globulins is not standardized until this moment, serial evaluation cannot be a guide for disease evolution or for the efficacy of therapy; it only remains a sign of the presence of these proteins, which are still not well known.