Heavy chain disease with monoclonal incomplete mu-heavy chains (mu-HCD) is a rare disorder usually associated with an underlying lymphoproliferative malignancy. Laboratory diagnosis of patients with mu-HCD is usually challenging and the monoclonal protein is not detected by electrophoresis in up to 75% of mu-HCD cases. We describe a patient with multiple malignancies in whom we detected and characterized monoclonal mu-heavy chains using immunofixation electrophoresis, capillary zone electrophoresis with immunotyping, and high resolution two-dimensional electrophoresis. The high resolution 2D electrophoresis enabled us to determine the molecular weight of the mu-heavy chains. The abnormal protein concentration in the serum was unusually high, 38 g/l measured in our patient is the highest reported value in the literature so far.