It has become more and more customary for a speaker invited to an international conference to hold his speech in a foreign language. Quite inevitably, speakers who do not master the language used often do not manage to present their speech in the most appropriate way from the point of view of linguistic production, thus impeding or constraining comprehension and, therefore, communication. Among the most commonly observable features of speech of this kind are segmental and prosodic deviations which can sometimes cause severe difficulties for interpreters. This study aims to investigate whether and to what extent such source-text (ST) presentation can affect interpreters’ comprehension skills and the semantic quality of their rendition in the target-language (TL). For this purpose, a number of interpreters were asked simultaneously to interpret relatively segmentally and prosodically degraded ST presented by a speaker not using his native language.