In this article, we examine the programmatic reactions to the rise of populist parties. It has been argued that populism is not necessarily the prerogative of populist parties; it has been adopted by mainstream parties as well. The article investigates whether populism is contagious. On the basis of the results of a content analysis of election manifestos of parties in five Western European countries (France, Germany, Italy, The Netherlands and the United Kingdom), we conclude that the programmes of mainstream parties have not become more populist in recent years. We find no evidence that mainstream parties change their programmes when confronted with electoral losses or successful populist challengers. Yet, we do find that populist parties change their own programmes when they have been successful: Their initial success makes them tone down their populism.