Renal and metabolic complications of tumor lysis during 46 episodes of remission induction chemotherapy were reviewed in 37 patients with American Burkitt's lymphoma. Azotemia occurred in 14 patients, preceding chemotherapy in eight. All of these patients had abdominal tumors. Pretreatment azotemia was associated with elevated lactic dehydrogenase (LDH) and uric acid levels, and sometimes extrinsic ureteral obstruction by tumor. Two patients required dialysis for uric acid nephropathy before chemotherapy was initiated. Following chemotherapy, major complications of tumor lysis (hyperuricemia, hyperkalemia and hyperphosphatemia) were associated with very large tumors, high LDH levels and inadequate urinary output. In patients undergoing diuresis and receiving allopurinol, hyperkalemia or hyperuricemia developed infrequently unless concomitant renal failure ensued. Hyperphosphatemia, which occurred only after chemotherapy, developed in 10 of 32 (31 per cent) nonazotemic and in all azotemic patients. Hemodialysis was required in three post-treatment patients for control of azotemia, hyperuricemia, hyperphosphatemia and/or hyperkalemia. Because of the potential for renal failure caused by precipitation of phosphate, severe hyperphosphatemia is an additional criterion for dialysis in patients with acute tumor lysis syndrome.