AbstractDNA synthesis and release was studied in unstimulated splenocytes of strains of mice known to develop spontaneous systemic lupus erythematosus (SLE)‐like disease and in non‐SLE age‐ and sex‐matched strains as well. Newly synthesized DNA was measured as total acid‐insoluble radioactive material present in cell pellet plus supernatant of unstimulated 0–72 h cell cultures [3H]thymidine‐pulsed, whereas DNA release was measured as amount of acid‐precipitable radioactivity found in supernatant of those cultures. In all strains known to develop spontaneous murine SLE the amount of newly synthesized DNA was 1.3–2.1‐fold increased when compared to normal strains studied concomitantly. Furthermore, a significant increase in DNA release into medium, unrelated to cell viability, was observed in those strains as well. These observations clearly demonstrate different metabolic rates of synthesis and release of DNA in murine SLE. This difference suggests the existance of an underlying mechanism responsible for extracellular DNA abundancy, which may be important for the formation of circulating DNA‐anti