BM 135586 = 1971–7–5, 1, until recently in private possession, is a hitherto unknown Neo-Assyrian letter belonging to the royal correspondence of Nineveh, and indisputably an important specimen of its genre. In 39 completely preserved lines, it contains a message to the Assyrian king Esarhaddon (680–669 B.C.) from his son Šamaš-šumu-ukīn, who at that time was the crown prince of Babylon. So far only three very short and fragmentary letters sent by Šamaš-šumu-ukīn in this office had been known, and they are now completely overshadowed by the new text, which is here published by permission of the Trustees of the British Museum. It is of dark grey-brown colour and measures 41 by 82 mm. For all further details concerning the tablet and the script I refer to the photographs and copy published on Plate XIX.