[영문]OBJECTIVES: We used participatory design methods to develop and test guidebooks about health care choices intended for 600 000 English-, Spanish-, and Chinese-speaking seniors and people with disabilities receiving Medicaid in California. METHODS: Design and testing processes were conducted with consumers and professionals; they included 24 advisory group interviews, 36 usability tests, 18 focus groups (105 participants), 51 key informant interviews, guidebook readability and suitability testing, linguistic adaptation, and iterative revisions of 4 prototypes. RESULTS: Participatory design processes identified preferences of intended audiences for guidebook content, linguistic adaptation, and format; guidebook readability was scored at the sixth- to eighth-grade level and suitability at 95%. These findings informed the design of a separate efficacy study that showed high guidebook usage and satisfaction, and better gains in knowledge, confidence, and intended behaviors among intervention participants than among control participants. CONCLUSIONS: Participatory design can be used effectively in mass communication to inform vulnerable audiences of health care choices. The techniques described can be adapted for a broad range of health communication interventions.