Are preferential trade agreements (PTAs) stumbling blocks or building blocks towards multilateral trade liberalization? We address this question by investigating the effects\ of the negotiation and implementation of PTAs on the use of antidumping (AD) (i.e., the most common form of contingent trade protection) by member countries against non-members as there has been a concurrent surge in regionalism and AD\ activity since the 1990s. Theoretically-derived empirical predictions are supported by the empirical analysis based on the 15 most intense users of AD. The results demonstrate that both the negotiation and the implementation of PTAs lead to fewer AD measures against non-member countries, except for members of customs-union agreements in force facing large import surges from non-members. Thus, our results highlight a building-block effect of PTAs on multilateral trade cooperation when it comes to AD protection.