This article examines the impact of the secret ballot on the market for votes at parliamentary elections in the 19th-century United Kingdom. I use a formal model of an exchange between a candidate and a voter to predict the impact of the secret ballot on bribe prices, the marginal effect campaign spending on candidates’ electoral prospects, and election turnout. I test these predictions against original data on bribe prices and campaign expenditures at over 500 parliamentary elections. The results are consistent with the argument that the secret ballot induced British parliamentary candidates to divert their campaign spending away from vote-buying and toward turnout-buying. These results point to the adaptability of political actors in the face of institutional changes.