The impacts of agrarian habitat types representative of the Northeast German Lowland (cereal fields, fallows, meadows) on the structure of the spider assemblage have been investigated on 16 study sites in the biosphere reserve Schorfheide-Chorin (Brandenburg, Germany). During 3 years (1995-1997) epigeal spiders were collected by pitfall traps (PT: n=8/10) and ground photo-eclectors (GPE: n=6). Altogether 40536 specimens belonging to 179 species were recorded, among them several taxa (18%) listed in the Red Data Book of Germany (n=29) and of Brandenburg (n=21). The highest biodiversity was recorded for pastures with 108/97 species (according to PT/GPE catches), followed by fallows (101/89) and fields (78/69). Within arable land most species were recorded on a biodynamic cereal field cultivated after a four-year period of fallow. Using estimates of niche width, Porrhomma microphthalmum, Erigone atra, Erigone dentipalpis, Savignia frontata and Meioneta rurestris were identified as characteristic species of cereal fields. Pelecopsis parallela, Oedothorax retusus. Trochosa ruricola and Alopecosa barbipes were characteristic of fallows and Thanatus arenarius, Trichopterna cito and Zelotes electus were typical of pastures. Only four species (Erigone atra, Meioneta rurestris, Pachygnatha degeeri, Pardosa palustris) were recorded on all study sites. Generally, most specimens and the highest activity biomass of spiders were manifested on grasslands and long-term fallows; the lowest levels were recorded for cereal fields. Fallowing of cereal fields seemed to promote the relative abundance and activity biomass of the spider assemblage immediately after taking the fields out of cultivation, whereas species diversity took longer to build up. A similar effect was obvious in cereal fields with a cultivation cycle that was interrupted by a one-year period of set aside. The dominance structure of the spider assemblage was clearly affected by the agrarian habitat types: While the relative abundance of linyphiid spiders increased from meadows to cereal fields, the dominance position of lycosids decreased in the same sequence of agrarian habitat types. As expected, diversity indices using estimates of α (log series) were lowest on cereal fields, and highest on extensively used pastures as well as long-term fallows, independent of the sampling method.