Pre-print, Working paper: This paper analyses the potentially defensive behaviour of successful innovators and its effect on aggregate R&D effort. It proposes a quality-ladders model that endogenously determines leader's technology advantages and who innovate (the leader firm or its competitors). Regulation can have either a positive or a negative effect on R&D intensity. It can be negatively associated to aggregate innovative effort in higly deregulated economies. In more regulated ones, where deterring strategies are constrained, it yields incentives to innovate. These predictions are consistent with data on manufacturing industries of 14 OECD countries between 1987-2003.