Argentine industrial growth beginning in the 1950's catalyzed migration from the poorest provinces, leading migrants to seek improved living conditions and better job prospects in the capital. Santiagueños (Santiago del Estero, northwestern Argentina) are the largest migrant group (ca. 250,000, including both Spanish-Quechua bilinguals and Spanish monolinguals) having settled mainly in Buenos Aires. Like other cases of syncretism and acculturation in the traditional values and ways of speaking in indigenous communities in the Americas due to long-term contact with European-dominated societies, the more powerful and prestigious Spanish sociocultural context surrounding the Santiagueño migrants has conditioned their framing of communicative practices, their language use and their attitudes towards both themselves and the Argentine society at large. This paper describes some ethnolinguistic effects of urban migration on Quechua-speaking Santiagueños dwelling in Buenos Aires such as language mixing, transfer from Spanish on all linguistic levels and variable competency loss in Quechua. The degree of the latter depends on factors like the age at migration and the strength of social ties to the Santiagueño community. Furthermore, an assesssment of migrants' language attitudes indicates a growing sociolinguistic differentiation between their Spanish variant and that spoken by non-migrants in rural sections of Santiago del Estero.