It is suggested that contrastive linguistics, the systematic comparison of two languages, be considered in the preparation of instructional materials and as a choice of teaching methods and techniques for training tranlators and interpreters. The contrastive analysis hypothesis suggests that the major source of errors committed by learners of a foreign language is the difference between concepts and linguistic patterns of the source and target language. Two studies of errors made by university students in translating are reported to support the use of contrastive analysis in training translators and interpreters. (JL)