THE contribution of mergers to the increase in industrial concentration raises important issues for economists, for economic historians and for governments' economic policies on mergers. While it is agreed that mergers have been very important in the UK since the I96os, there is no agreement on the size of this contribution in the inter-war period. In particular Drs. Hannah and Kay  do not accept the arguments of Hart . The only thing to do is to explain, as dispassionately as possible, why I think they are wrong and leave the readers of this journal to judge for themselves.