When many symptoms and laboratory findings occur together without a specific known cause, the grouping is called a “syndrome.” Mixed cryoglobulinemia (MC) is a syndrome characterized by bleeding spots under the skin, weakness, painful joints, and specific abnormalities in one or more organs of the body. A distinguishing feature of MC is the presence of more than the normal number of B lymphocytes (a white blood cell that makes proteins, known as immunoglobulins, that protect us from infection). MC occurs frequently in people infected with hepatitis C virus (HCV). Since HCV infects both liver cells and B lymphocytes, HCV itself may cause accumulation of B lymphocytes. Exactly how this happens is unknown, but the virus sometimes is associated with a rearrangement of chemicals that make up the genetic material in the B lymphocytes (bcl-2 rearrangement). This bcl-2 rearrangement may prolong the lifespan of B lymphocytes and lead to excessive accumulation of these cells in the body. It may also predispose to cancerous transformation of these cells, a condition called lymphoma.