The situation in the German-speaking part of Switzerland is known as "medial diglossia". In spoken language, different alemannic dialects are used, while Standard High German is the medium in written language. These dialects vary linguistically as well as in their sociolinguistic status. The dialects of urban areas are used by many speakers and are considered to be comprehensible for everyone. The dialects of peripheral areas are spoken by few persons and are regarded as difficult to understand. We focus on the question if and how migrants with "difficult" dialects who move to an urban area adjust the way they speak: Do they keep their own dialect or do they take on the dialect of their new surroundings? What kinds of changes occur? How can these changes be correlated to sociolinguistic factors like dialect loyality and social network structure? We are interviewing permanent migrants who have lived in the city and agglomeration of Berne for quite some time and, as a contrastive sample, people who arrived in Berne just recently. While the permanent migrants were interviewed once, the latter group has been interviewed in regular intervals over a period of two years in order to incorporate the crucial logitudinal component which allows for the observation of linguistic change in progress. We compared a speaker's dialect as used in the interviews with his or her source dialect as well as with the target dialect, with the corpus of the Linguistic Atlas of German-speaking Switzerland serving as authoratative reference. Based on the assumption that every speaker has recourse to a linguistic repertoire which can be adapted consciously or subconsciously to serve the felt needs in a particular situation, we scrutinize dialectal variation in the speech of both long-term and recent migrants in two dimensions: during one interview session, i.e. within a 60-80 minute time frame during which various levels of familiarity and formality of and emotional involvement in the interview are created (both naturally as well as by conscious strategies on the part of the interviewer), and longitudinally, i.e. over the period of two years for recent migrants and x years for longterm migrants (where x>3). We expect to find a correlation between the degree of dialect loyalty on the one hand and the intensity of the contacts to the place of origin as well as characteristics of the social networks on the other hand. We presume that persons with a high degree of dialect loyalty keep closer ties to their native place and have more contacts to fellow migrants from the same native place than persons with a low degree of dialect loyalty. Our corpus consists of roughly 150 narrative interviews with a length of approximately 80 minutes each, 150 written questionnaires to document socio-biographical information as well as relevant information on social networks and attitudes towards dialects. Three kinds of transcriptions of these data are available: Keyword content transcriptions, discourse analytical transcriptions using an adapted version of the Dieth system for the writing of Swiss German dialects, and selective phonetic transcriptions using IPA. Keywords: sociolinguistics, dialectology, dialect loyality, dialect change, languages in contact, loyality, variation grammar, social networks