The present study replicates an experiment by Rheinberg and Vollmeyer (2003). In accordance with flow theory, these authors were able to show that the experience of flow while playing a computer game depends on the fit between challenge and skill, In our study, 76 university students played the computer game "Roboguard" at a level with optimal fit between challenge and skill and at two levels with low fit (too easy, too difficult). In contrast to Rheinberg and Vollmeyer, the computer game was modified in order to have less extreme easy and difficult play levels. In the case of the difficult level it was now possible for the participants to have at least minimal success, whereas in Rheinberg and Vollmeyer's study the participants were almost unable to act. The results showed the expected effects for the easy and optimal levels but not for the difficult level. In contrast to expectations, the participants indicated high degrees of flow at the difficult level, A possible explanation for this finding is that extremely high demands in a game situation do not reduce the experience of flow under certain conditions. We concluded that games such as Roboguard are not suitable for flow research in general, but only for specific research questions.