Brefeldin A has proven to be a useful pharmacologic tool, which, when added to mammalian cells, results in a block in secretion as well as the structural disruption of specific intracellular organelles. In spite of our understanding of some of the biochemistry underlying the action of brefeldin A, the most proximal molecular target(s) of the drug remain elusive. In attempting to address this problem, a genetic approach will undoubtedly prove useful and complementary to the biochemical identification of such a site(s). As a result of the relatively resistant nature of wild-type Saccharomyces cerevisiae to brefeldin A, an approach utilizing yeast genetics has not been possible. We report the selective sensitivity of three drug-sensitive strains of S. cerevisiae (ise-1, ISE-2, and erg6) with enhanced membrane permeability allowing uptake of brefeldin A. Upon addition of the drug, growth is dramatically inhibited and invertase secretion is rapidly, specifically, and reversibly blocked at the level of the endoplasmic reticulum. In addition, only structural analogues of brefeldin A effective in mammalian cells are active in these yeast strains.