Five experiments are reported in which the picture naming performance of bilingual speakers in a language-switching task was explored. In Experiment 1, Spanish learners of Catalan and Korean learners of Spanish were asked to perform a switching task between their first and dominant language (L1, Spanish or Korean) and their second language (L2, Catalan or Spanish). For these two groups switching from the weaker language (L2) to the more dominant language (L1) was harder than vice versa. This asymmetrical switching cost was not present when highly proficient Spanish--Catalan bilinguals performed the task either in their two dominant languages (Experiments 2 and 3) or in their dominant language (L1) and in their much weaker language (L3 English; Experiment 4). Furthermore, highly proficient bilinguals showed faster naming latencies in their weaker languages (L2 and L3) than in their dominant language (L1). Experiment 5 tested whether a bias in the triggering of lexicalization is at the basis of such a difference. Together these results reveal that the switching performance of highly proficient bilinguals does not seem to be subject to the same mechanisms as that of L2 learners.