A clinical evaluation of the intradermal DNA-test was carried out on a series of patients with untreated or with treated definite systemic lupus erythematosus (SLE), or with suspected SLE with or without circulating antinuclear factors. A saline solution of a commercially available DNA-preparation was used. The course of the DNA reaction was followed for 24-48 h after the injection. All nine cases of untreated definite SLE had a positive DNA test 6 h after the injection, and eight cases a positive result at 24 h. All seven patients with definite SLE who were on low-dosage systemic steroid treatment had a clinically positive. DNA test at 6 h. In all except one of these cases the test was still positive at 24 h. All five patients with definite SLE on antimalarial treatment had a positive test at 6 h which had become negative at 24 h after the injection. Eleven of the twelve patients with suspected SLE and circulating antinuclear factors had a positive DNA test at 6 h, which in nine cases persisted for 24 h. On the other hand, of the eleven ANF negative patients with various connective tissue diseases five had a positive test at 6 h. In only one of these cases it persisted for 24 h. Two of the eighteen control patients with various dermatoses exhibited a positive test at 6 h, and in one of these the positive reaction persisted for 24 h. It is concluded that the intradermal skin test using native DNA is a useful diagnostic tool for the detection of SLE when the reaction is followed up for 24 h. Antimalarial treatment seems to decrease skin reactivity to native DNA.