In four studies, we obtained evidence for the reliability and validity of a 2I-item scale designed to measure a new theoretical construct: individual differences in the motivation to acquire relationship-threatening information (hereafter, MARTI). Study 1 provided evidence for the MARTI scale's reliability and discriminant validity, revealing that it was reliable and not significantly correlated with measures of the Big Five personality traits, adult attachment styles, or more general social orientations. Studies 2 and 3 provided evidence for the scale's convergent and discriminant validity, showing that dating partners with higher MARTI scores (i.e., those who were more motivated to acquire relationship-threatening information) scored lower in relational trust and reported engaging in more "suspicion behaviors." Study 4 provided behavioral evidence for the scale's predictive validity, revealing that (a) dating partners with higher MARTI scores were more likely to break up within 5 months, and (b) the breakup rate was most pronounced for dating partners who scored higher on the scale and who also reported being less close. We discuss how this new construct and measure can be used to study important relationship dynamics.