This study is an empirical investigation into horizontal regional variation in the Modern Standard Arabic of radio news bulletins. After first determining the position of Modern Standard Arabic within the Arabic language setting, which has been described in terms of, among other things, diglossia, triglossia and quadriglossia, the consequences which these descriptions have on the methodological level are analyzed. For this study a corpus-linguistic approach was chosen, requiring the compilation of a text corpus of radio news bulletins from linguistically very different countries, Algeria, Egypt and Saudi Arabia. The completely transcribed corpus of approximately 320,000 words was tagged primarily on the word level, using the traditional, mixed grammar as a reference point. Various computer applications were then developped to explore the corpus. The emphasis in this study was on the synchronic description of the use of complementary particles with reference to contemporary Standard Arabic grammar. In general, the investigation attests to great uniformity among the three countries on the syntactic level, but it also reveals that with particles of a similar function an important shift in function has occurred as compared to the descriptions of these particles in classical Arabic grammar.