The clinical studies about the electrolyte abnormality (EA) in patients with malignant lymphoma (ML) are rarely reported. We analyzed the EA and renal insufficiency in 123 patients with ML between June. 1976 and Jan. 1989; 8 patients with Hodgkin's disease, and 115 patients with non-Hodgkin's lymphoma (NHL). Before treatment, the incidence of the EA was 24.2% and hypercalcemia, hypocalcemia, and hyperkalemia were predominant. After treatment it became to 74.7% and the number of hyponatremia and hypokalemia increased. The incidence of proteinuria and renal insufficiency (serum creatinine above 1.5 mg/dl), were 7.3% and 2.4% before treatment, and became to 26.8% and 26.8% after treatment, respectively. There was a significant difference between two groups with and without the EA before treatment as for serum lactate dehydrogenase (LDH) levels (p less than 0.01), clinical stages (p less than 0.05) and the incidence of bone marrow involvement (p less than 0.01). In 34 autopsied cases, 3 cases showed massive renal involvement and about a half of cases showed various renal changes. The EA before treatment was caused by extrarenal factors, because the incidence of proteinuria and renal insufficiency were almost same to healthy controls. And renal factors play an important role on the E.A after treatment. Above results suggest that the EA before treatment indicates the progress of malignant lymphoma and the EA after treatment means not only the progress of the disease but also therapy-related renal damages.