The nitroblue tetrazolium (NBT) dye test was performed in 25 cases of lymphoma. Four of six patients with active, untreated lymphoma and with no evidence of bacterial infection had positive NBT tests (more than 10% of neutrophils reduced the dye to formazan). One of these four patients had occasional negative tests. The NBT tests of 17 patients with lymphoma who were either receiving chemotherapy or were in untreated remission were negative (10% of neutrophils or less reduced the dye). Two other patients had intermittently positive NBT tests. One had active disease and was on maintenance chemotherapy. The other was in clinical remission and was not on therapy. The tests of 21 normal controls were negative. The NBT test can be positive in lymphomas uncomplicated by infection and may be suppressed by chemotherapy or corticosteroids.