Abstract
A 63-year-old woman presented with Raynaud's phenomenon and extensive cold-induced livedo reticularis. A skin biopsy showed no abnormality of the blood vessels but the blood contained high titres of a very unusual autoantibody against the M blood group, most active at low temperatures. An IgM cryoglobulin was detected, and anti-M activity was found in this fraction. The cells of the patient were grouped as MM. The direct antiglobulin test was positive due to C3 component of complement bound to the red cells. The haematological and biochemical results indicate a mild haemolytic process, which is at present well compensated.