In this paper we present results from an controlled experiment on incentive use during the reminder process for recruitment into the German Internet Panel (GIP), an online panel based on a probability sample. Gaining consent and cooperationfrom respondents selected to be future panel members is a difficult task, dropout can occur at many stages of the survey process. To help maintain cooperation of respondents during this process, cash incentives can be used.A randomized experiment conducted during the recruitment into the German Internet Panel allows us to examine of the effects ofincentive treatment on recruitment success. Following a face-to-face recruitment interview, respondents were invited to sign up online and register for the GIP via mail. If respondents failed to sign up, a reminder letter was sent. With this letter, a random group of the target respondents received a 5 Euro cash incentive. The main effect of the experiment is plain and simple, cash incentive group was more likely to register to the panel. However, using data from the recruitment interview on sociodemographics, voting preference and income we can go beyond looking at signup rates. We can observe possible biases and differences in sample composition obtained in the online panel in respect to incentive treatment. In addition, total recruitment cost can be compared between the incentive group and the control group. With these results we can describe the effects of incentive use in a reminder process both on cost as well as quality of the resulting sample.