The rate of successful health care innovation implementation is dismal. Middle managers have a potentially important yet poorly understood role in health care innovation implementation. This study used self-administered surveys and interviews of middle managers in health centers that implemented an innovation to reduce health disparities to address the questions: Does middle managers' commitment to health care innovation implementation influence implementation effectiveness? If so, in what ways does their commitment influence implementation effectiveness? Although quantitative survey data analysis results suggest a weak relationship, qualitative interview data analysis results indicate that middle managers' commitment influences implementation effectiveness when middle managers are proactive. Scholars should account for middle managers' influence in implementation research, and health care executives may promote implementation effectiveness by hiring proactive middle managers and creating climates in which proactivity is rewarded, supported, and expected.