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Fitting hearing aids to open ear canals, in spite of its many benefits and increased popularity, is particularly prone to feedback problems. The present study examined the system responses of the feedback path and how effective the feedback signals can be cancelled under the open-canal condition. Compared to a traditional fitting method with earmolds, the open-canal fitting has a smaller amount of usable gain due to a minimal sound attenuation (27 dB) in the open canal. Furthermore, the open-canal fitting appears to have no advantage over the traditional method in the amount of extra usable gain (15 dB) that the current feedback-cancellation system provides. Significant improvement to the feedback-cancellation system, either from increased signal-processing power or from the improvement in design based on the knowledge of the open-canal characteristics, will be needed to extend the benefits of the open-canal fitting method to patients with more than a moderate hearing loss.