This paper tackles some of the problems encountered while developing the French-English version of the Siemens-Nixdorf METAL® computer-assisted translation system. The first part deals with the general problem of delimiting lexical units and the second part describes a few concrete translation problems and the solutions that have been adopted in this experimental transfer-based system. The role and importance of the lexicons is stressed, focussing more specifically on the possibility the lexicographer is given to manipulate complex structures and to control the translation process directly.