This study investigates the extent to which strong relationships between a firm and its key suppliers promote effective new product introduction. Building on the relationship marketing literature, we identify self-enforcement and interdependence as two contingent relational variables that influence the strength of the buyer-supplier relationship. We use data from a survey of 2331 manufacturing firms in China to test the hypotheses. The results show that strong relationships with key suppliers correlate with product introduction success and that this positive effect is contingent on the two relational variables identified. Self-enforcement strengthens the utility of strong supplier relationships for these Chinese manufacturers, and buyer-supplier interdependence enhances this relationship.