Influence and persuasion are related, fundamental constructs in interpersonal communication. Both display the relationship qualities of interdependence, bidirectionality, reciprocity, and multiple levels of analysis. Yet, empirical validation of these relationship qualities is lacking, largely due to an absence of appropriate methods and statistical procedures. This article uses the family social relations model (SRM) to test for the personal relationship qualities of influence and persuasion in the family decision-making context of buying a new car. New relationship measures of influence and persuasion were developed because, historically, measures have been at the individual level. The sample size of 110 families proved sufficient for stable parameter estimates. The results uncovered patterns in the relationship qualities of influence and persuasion across 3 decisions families make when buying a new car (i.e., how much to spend, car model choice, final decision). The findings confirm that both influence and persuasion are truly relational. The novel use of the model across decisions allowed the patterns of relationships among family members to be compared, and demonstrated the importance of the relationship qualities of influence and persuasion in decision making. Predictions were examined across decisions as well so as to check the consistency of hypotheses. The results provide further insight into the meaning of influence and persuasion, and of SRM terms.