The role of other customers play in determining a service customer's experience has emerged as important and received growing attention recently. Yet, the role of companions has not. In this study, using the healthcare setting as our research context, we explore how companions affect the patient throughout the service encounter process. Specifically, we propose that the quality of the role companions play affects the quality of the role patients play, which eventually affects the perceived quality of the service patients receive from the healthcare provider. In other words, we propose companions as a source of improving customer perceptions of service quality. Further, in an effort to define the desirable type of companions, we propose that the quality of relationship between the customer and the companion will influence the customer perception of the companion role quality. We also propose that the patient's stress level will moderate the effect of companion's role on the patient's role. In order to measure the quality of the role a companion and a patient play respectively, we first developed a scale for each by comprehensively compiling existing scales for each. We adopted the existing SERVQUAL items to measure perceived service quality. We adapted existing scales for measuring the quality of relationship between the patient and the companion and for measuring the patient's stress level. We plan to conduct a self-administered survey among the patients at a major university hospital in Seoul, Korea. We will analyze the collected data through a factor analysis, an analysis of variance, and a structural equation modeling approach. Findings of the current study will contribute academically by extending the research stream in viewing other human factors in the service setting as influential factor in determining the customer perception of service quality. Managerially, our study will contribute by demonstrating the importance of ensuring that companions play their role well throughout the service encounter process and also by presenting a comprehensive scale to measure the companion's role.