A suspension of bentonite particles sensitized with calf thymus DNA is flocculated when exposed to the serum of patients with systemic lupus erythematosus (SLE). Eight patients with active SLE were positive to this test at titers of 18 to 1:512; 2 of 5 patients with SLE in remission were positive at 1:2 and 1:4. Six patients with rheumatoid arthritis and positive lupus cell preparations were negative to the DNA-bentonite test. An additional group of 132 individuals (78 with other diseases and 54 healthy adults) was negative to this test. In comparison, (1) the lupus cell test appears to be more sensitive than the DNA-bentonite test, but (2) the DNA-bentonite test is more specific than the lupus cell test,.