Since the advent of green-fluorescent protein (GFP) technology there has been an explosion of interest in applying this molecule to cell biology. This review summarizes new insights in secretory membrane traffic obtained by the use of GFP fusion proteins. Transport steps between the endoplasmic reticulum and the Golgi apparatus, intra-Golgi traffic, and transport from the Golgi to the plasma membrane are discussed. In addition, insights into the dynamics of the Golgi compartment in plant cells and in mitotic mammalian cells have been included. We conclude that membrane traffic in the secretory pathway appears to be much more dynamic and diverse than previously thought and that GFP promises to be a powerful means to unravel these complex processes.