This article describes an experimental study which measured the extent to which the monotonous intonation of an interpreter can cause receivers to negatively evaluate the resulting interpretation, particularly when compared to the non-monotonous interpretation of another interpreter. In addition, the study analyses the emotional inferences made by the receivers of the monotonous intonation, and its effect on their assessment of the interpretation. The article also describes the results of various discussion groups and focused interviews which formed part of the study. This type of qualitative research methodology was found to provide a better explanation of certain aspects of the complex assessment process and to offer a more accurate insight into the way receivers evaluate simultaneous interpretations.