The idea for the present study originated from the importance for any interpreter to be able to correctly transpose numerals from and into any of his working languages, as well as from the high number of errors commonly related to this particular kind of performance. This experimental study is mainly devoted to the analysis of the cognitive mechanisms involved in the processing of numerals in the oral, phonologic modality of expression. This has been done by means of the special task of simultaneous interpretation from one language into another wherein apart from an initial phase of comprehension and a final one of production of verbal material, there is, somewhere in between, the phase of translation of the numeral into a language other than that of presentation.