Two patients with lymphoplasmacytic lymphoma, and monoclonal proteins of IgM in one, and IgG and lambda light chains in the second patient, nephrotic syndrome and acute renal failure are reported. A 58-year-old man previously treated for pre-B acute lymphoblastic leukemia, developed 3 years later nephrotic syndrome as a complication of lymphoplasmacytic lymphoma and high-paraprotein IgM kappa type. Immunofluorescent analysis of kidney biopsy showed extensive IgM and light kappa chain deposits, which caused membranoproliferative glomerulonephritis. Treatment with cyclophosphamide was ineffective and patient died 2 months later. The second patient is a 42-year-old female diagnosed with lymphoplasmacytic lymphoma and paraprotein IgG lambda type. The course of the disease was fulminant with developing nephrotic syndrome and fatal acute renal failure. Immunofluorescent and light microscopic studies of kidney biopsy showed signs of immunotactoid glomerulonephritis with deposits of IgG and C3. Hemodyalises and cytostatic therapy were without response and she died after 45 days.