During the last decade a lot of attention has been paid to instruments of relationship marketing (MR) aimed at retaining and developing customers. Among these, retail loyalty cards have received considerable attention. A wide body of research has focused on the effects of MR on customer purchasing behaviour. Notwithstanding such considerable research efforts, however, we still have mixed evidence about the effectiveness of MR, and scholars are debating about their future. In this paper, we intend to contribute to the current debate by pointing on the effects of inter-firm networks of marketing alliances which we label loyalty networks on the effectiveness of MR in retail settings. Previous research has focused mainly on stand alone MR, and has not considered the impact of collaborative structures on the outcomes of such programs; however some scholars have argued that networking strategies may improve the performance of MR. Drawing form previous research on inter-firm networks and complementarity, our hypothesis is that the degree of overlapping between partners’ networks impact positively on the effectiveness of the MR at the store level, expressed in terms of share of active cardholders collecting points at the different partners’ stores. Hypotheses are tested on a dataset of 52 stores of a primary retail chain in the region surrounding Milan (Italy), which has developed a partnership with a gas station chain located in the same area. The data shows a positive relationship between the overlap of the networks and the outcome of the loyalty program at the store level. Such evidence is discussed with reference to the existing research on MR, inter-firm networks, and marketing complementarity. Keywords: Network fedeltà; sovrapposizione tra reti; efficacia programmi di fidelizzazione; retail.