Modern interlingual situations are becoming ever more varied and complex. Interpreters are thus confronted with increasingly diverse situations that require a global approach to the communicative process. This article exemplifies one such situation, namely the experience of interpreting at an Immigration Detention Center in Las Palmas de Gran Canaria, Spain, in November-December 2001. Several factors are found to condition the communicative relationship between immigrants and the State, with the extra-linguistic variables playing as important a role as the linguistic ones. This is especially true in view of the significant power structures involved, which have consequences for the low social prestige of both immigrants and interpreters in such settings. Power relations also structure contextual constraints at professional, legal, translational and communicative levels. A semiotic approach is considered able to cover this wide range of variables and may ultimately lead to a more global understanding of the interpreting profession.