The serum uric acid ( SUA ) was measured in 21 malignant lymphoma (ML) patients and 11 multiple myeloma (MM) patients. Hyperuricemia, represented by a SUA level over 8.0 mg/dl, was found in 19.1% of the patients with ML and 9.1% of those with MM Hypouricemia (SUA below 2.5mg/dl) was noted in 4.9% and 9.1% of the patients with ML and MM, respectively. The mean SUA levels in ML were not significantly different in terms of sex, type of histology and stage of the disease. Moreover, no correlation was seen between the mean SUA levels and serum LDH activity in ML. After chemotherapy, nearly parallel decreases were observed in SUA and serum LDH in ML. The mean SUA levels were highest in Bence-Jones type among subtypes of immunogloblin in MM. The mean decrease in SUA concentration after chemotherapy without allopurinol was about 1.0 mg/dl in both MM and ML. There were no cases. There were no cases of acute hyperuricemic renal failure in either ML or MM.