A new Stylosanthes species with potential as a pasture legume for acid, infertile soils is described. Its natural distribution is limited to Central/Eastern Brazil. Between 1975 and 1982 a germplasm collection of ? 100 accessions was assembled, principally by EPAMIG and during joint EMBRAPA/ClAT collection expeditions in the Federal District and the states of Goiás, Bahía and Minas Gerais. In preliminary evaluation studies conducted at Sete Lagoas, Minas Gerais, Brazil, and Quilichao, Cauca, Colombia, the collections showed excellent adaptation to soil acidity and high Al levels (pH 3.8 and 88% Al saturation at Quilichao), and many of the accessions proved to have very low phosphorus requirements. At both testing sites a large proportion of the collections were highly resistant to anthracnose. Dry matter productivity was a very variable plant character in both locations; germplasm material originating from the Brasilia/Goiás region proved to be particularly productive. Contents of crude protein, P and Ca in the Quilichao collection were within a range considered normal for Stylosanthes whereas in vitro dry matter digestibility was high. The need to collect more germplasm of S. macrocephala is discussed, and several regions are identified for further collections.