Changes in serum alkaline DNase activities might predict the therapeutic response in various malignant diseases. A decrease in serum alkaline DNase activity within days from the onset of therapy has been related to tumour necrosis and may be a possible sign of clinical response to effective treatment. To study if changes in serum alkaline DNase activity could be induced by non-tumour related tissue destruction, sera were collected on several occasions perioperatively in 18 patients undergoing surgery for benign gynaecological disease. Thirty apparently healthy women served as the control group. A significant decrease (P less than 0.001) in serum alkaline DNase activity was observed after an overnight fast in both groups of women. In contrast to the control women, the operated patients showed a significant decrease (P less than 0.001) in serum alkaline DNase activity throughout the operative period and 1 week postoperatively. We conclude that serum alkaline DNase activity is influenced by dietary factors as well as surgical trauma. These factors may limit the clinical usefulness of SADA in patients with cancer.