We study the wealth effects created by bank mergers and acquisitions in the U.K. bank merger wave from 1885 to 1925. Due to the confidential nature of merger negotiations this setting allows us to precisely measure the wealth effects of M&As in a laissez-faire environment, avoiding measurement error caused by the timing of information release. In addition, since over 99% of all announcements resulted in a completed merger we are able to avoid the truncation dilemma. We find positive wealth effects for bidders (0.7%-1%) and targets (6.7%-8%) over the announcement month. Joint with Fabio Braggion and Lyndon Moore.