Recent studies suggest that anti-DNA antibodies may arise from the immune response to a complex of DNA and a DNA-binding protein. One of the protein targets frequently recognized by anti-DNA antibodies is the enzyme DNAase I. To investigate the possible role of DNAase I in the induction of anti-DNA antibodies, we immunized mice with a complex of DNA and DNAase I. Mammalian double strand DNA was crosslinked with DNAase I by ultraviolet light (UV) treatment and emulsified in complete Freund's adjuvant. BALB/c mice were immunized at the base of the tail with the DNA-DNAase complex, boosted after 2 weeks with the immunogen in incomplete adjuvant and bled one week after the boost. Control mice received UV treated DNA in adjuvant. In one-third of the mice immunized with the DNA-DNAase complex, IgG anti-DNA antibodies were detectable in serum; the antibodies reacted with single and double strand DNA. No anti-DNA response was elicited by immunization with DNA alone. These data show that immunization with a DNA-DNAase complex can induce anti-DNA antibodies in non-autoimmune mice strains and suggest that DNA-binding proteins may act as carriers in the immune response that leads to anti-DNA antibody production.