Numerous plasma cells were transiently found in the urine of a patient with multiple myeloma. The patient was in acute renal failure, and she had K-type Bence-Jones proteinemia and proteinuria. A slide of stained urine sediment showed cells with freatures characteristic of plasma cells. Their cytoplasm was highly reactive with anti-K antiserum on immunofluorescence, suggesting that these were myeloma cells.