In XPRESS, a randomised study of prophylactic heparin versus placebo in adult severe sepsis patients, all treated with drotrecogin alfa (activated), serious bleeding rates were consistent with those observed in previous studies over the treatment period of 0-6 days, and prophylactic heparin did not increase the risk of serious bleeding compared to placebo (2.3% vs 2.5%, respectively), including CNS bleeding (0.3% on both arms).