Building on evidence that Latino voters participate at higher rates when co-ethnic candidates appear on the ballot, we report the results from a field experiment examining whether co-ethnic policy leadership can produce similar mobilization in direct democracy elections. The study features a direct-mail campaign conducted during California’s 2010 statewide primary election aimed at mobilizing Latino voters. The experiment included variation in the language of the message sent to voters and the extent to it emphasized the pivotal role played by a prominent Latino official in placing the policy on the ballot. We find that mobilization messages are most effective when they target voters using their preferred language, at least for English-dominant Latinos. By contrast, our experiment yielded no evidence that co-ethnic policy leadership increased voter turnout, although we do show that female voters participate at higher rates when the mobilization campaign prominently features a high-profile female official. These divergent effects provide lessons for the study of ethnic political participation and for the design of effective mobilization campaigns aimed at boosting Latino turnout.