It is well-known that the studying abroad experience, hence immersion, can boost the learning process and the acquisition of the L2, however, little is known about the changes in the L1. This might be because these effects are less detectable. Linck et al (2009) tested the hypothesis that immersion facilitates L2 learning because it enables adult learners to attenuate the activity of the L1. They compared the performance of two groups of native English-speaking university students at an intermediate level of acquiring Spanish as an L2: one group learned the language only in the classroom, while the other spent 4 months in Spain immersed in the language. The results showed that the students in the immersion situation performed worse on L1 in both the production (verbal fluency) and comprehension (translation equivalence perception) tests, the latter result being measurable 6 months after returning home. Motivated by these findings, Baus et al. (2013) were interested in the effects of L2 immersion on L1 production, in particular how lexical frequency and cognate status modulate these effects. They basically tested whether the immersion effects are due to the decreased frequency of use or due to the interference produced by the L2. The weaker links hypothesis (Bialystok et al.; 2008 Gollan et al., 2005) explains the frequency effect, that is, the links between semantics and phonology become weaker over time as they are less used (e. g. in L2 immersion the L1 is less practiced). In this regard a larger effect for low-frequency (and non-cognate) words was expected by the authors as the links were already weaker before immersion than for common words. The interference is depicted by Green’s Inhibitory Control Model (ICM, Green, 1998) according to which lexical selection in the target language can be achieved by inhibiting the corresponding item in the non-target language. In an L2 environment this means constant inhibition of L1 representations, so in the study an overall inhibition of the L1 vocabulary was expected. To test these hypothesis, German Erasmus students (N=50) immersed in a Spanish speaking environment (Tenerife, Spain) for a period of six months were studied. The students were tested at the beginning and towards the end of the exchange program with a picture naming task and a fluency task (among others). The results clearly show that after a few months immersion in the Spanish environment the availability of the L1 has reduced and typically for low-frequency and non-cognate words which confirms the weaker links hypothesis. No difference was found in the fluency task between the two periods which is often the case in attrition studies: “all attempts to account for within group variation have failed so far”. (Schmid–Köpke, 2009, 213.) In sum, it seems that the frequency of use of the L1 and the L2 during the immersion period and the (phonological) similarity between the two languages can account for L1 word access and retrieval.