Nat. Med. 10, 524–529 (2004). Three sentences in this article appeared incorrectly. On p. 524, in the second paragraph after the abstract, the fifth sentence should read “ADP circulates in serum as low-molecular-weight dimers of trimers and high-molecular weight complexes5.” On p. 525, in the first paragraph in the right column, the second sentence should read “We also injected ADP (2 μg/g) or PBS i.v.