ABSTRACT: When learning English, Brazilian learners tend to replace the consonant sound /θ/ with /s/, /t/, or /f/, and replace /ð/ with /z/, /d/, or /v/ (REIS, 2006). The objective of this study is to analyze if the non-target pronunciations of these consonant sounds by Brazilians hinder comprehensibility, as judged by English native speakers. Ten speech samples containing the pronunciation of the sounds /θ/ and /ð/ by Brazilians were collected and presented to a group of eleven native English speakers. The listeners were asked how difficult it was for them to understand the words that contained these consonant sounds. The results indicate that non-standard pronunciations of the interdental fricative sounds by Brazilians affect comprehensibility. KEYWORDS: comprehensibility; English interdental fricatives; Brazilian learners.