The soils are seasonally or permanently saturated in the moist grassland savanna, locally known as Campo Limpo Umido. Soil moisture variation seems to determine spatial distribution of communities. The objective of this study is to analyse the relationship between environmental variables and the patterns of spatial distribution of species in the herbaceous-subshrub layer of an area of moist grassland at the Agua Limpa Farm, Brasília, DF (15 degrees 56' to 15 degrees 59' S and 47 degrees 55' to 47 degrees 58' W Gr.). An area of 400 x 400 m was divided into four sections of 200 x 200 m where four transects were randomly sampled. A line intercept method was adopted for the phytossociological study. Superficial soils samples (0-20 cm) were collected for chemical and textural analyses. Gravimetric soil moisture was measured quarterly during the study-year. A total of 85 species in 67 genera and 24 families were found. The diversity was high, Shannon's index, H', was 2.60 nats.cover(-1). Floristic composition of the transects in soils with a high gravimetric soil moisture and high content of organic matter and sand differed from those transects in soils with a lower gravimetric soil moisture indicating seasonal variation. A Canonical Correspondence Analysis (CCA) showed significant correlations between soil texture and soil moisture features and species distribution. Gravimetric soil moisture, organic matter, clay, silt and sand were significantly correlated to species distribution in the moist grassland determining mosaics in the vegetation.