This paper reports on a research project, the first part of which studied via focus groups the perceptions of a Nordic bank’s customers towards various personalized marketing messages in their online bank. Authors employed the Elaboration Likelihood Model (ELM) of persuasion as a theoretical framework. In the second part, a 9-week field experiment at an online bank was conducted. In this experiment, customers were shown personalized banner advertisements when they logged in to their online bank service. Three different types of financial products were promoted to three groups of customers.