Brefeldin A is a potent inhibitor of cell growth first described in 1958, then independently rediscovered by several groups as a potent active in a broad range of bioassays. Brefeldin has antiviral, antibiotic, antifungal, antitumor and herbicidal activity. Early studies on the mode of action of brefeldin identified inhibition of protein and nucleic acid synthesis by disruption of the Golgi apparatus. The precise molecular target is a subset of Sec7-type GTP exchange factors (GEFs) that activate a small GTPase, Arf1p, an integral component of protein trafficking and signalling.