Freezing of gait is a phenomenon common in Parkinson's patients and significantly affects quality of life. Sensory cues have been known to improve walking performance and reduce freezing of gait. Visual cues are reported to be particularly effective for this purpose. So far, sensory cues have generally been provided continuously, even when currently not needed. However, a recent approach suggests the provision of cues just in the case that freezing actually occurs. The arguments in favor of this "on-demand" cueing are reduced intrusiveness and reduced habituation to cues. Here, we analyzed the effect of visual cues on the number and duration of freezing episodes when activated either just "on-demand" or continuously and compare it to the baseline condition where no cue is provided. For this purpose, 7 Parkinson's patients regularly suffering from freezing of gait repeatedly walked a pre-defined course and their reaction to parallel laser lines projected in front of them on the floor was analyzed. The results show that, in comparison to the baseline condition, the mean duration of freezing was reduced by 51% in continuous cueing and by 69% in "on-demand" cueing. Concerning the number of freezing episodes, 43% fewer episodes were observed for continuous cueing and 9% less episodes for "on-demand" cueing.