Phakopsora pachyrhizi is a fairly new pathogen in South America and has become a serious threat for soybean production in the region (3). During May 2004, soybean (Glycine max) leaves with rust symptoms were observed on an experimental trial at La Estanzuela, National Institute for Agricultural Research in Colonia, southwestern Uruguay, on late-maturing genotypes (R7 stage). Small, necrotic, reddish brown lesions, suggestive of soybean rust, were detected on the upper surface of leaves. Uredinia and urediniospores were found on the underside of the leaves.