Internet advertisements are an increasingly common form of mass communication and present fresh opportunities for understanding enduring questions about political persuasion. However, the effects of online ads on electoral choice have received little scholarly attention. We develop a new field experimental approach for assessing the effects of online advertisements and deploy it in two studies. In each study, candidates for legislative office targeted randomly selected segments of their constituencies for a high volume of Facebook advertising. Recall of the ads, candidate name recognition, and candidate evaluations were measured with ostensibly unrelated telephone surveys after weeklong advertising campaigns. Voters randomly exposed to the ads were in some cases more likely to recall them but no more likely to recognize or positively evaluate the candidates they depicted. From a theoretical standpoint, these findings suggest that even frequent exposure to advertising messages may be insufficient to impart new information or change attitudes.