The dorsoventral axis of the Drosophila embryo is specified by a ventral-to-dorsal concentration gradient of the NF-κB/REL transcription factor Dorsal in the nuclei of the syncitial embryo. This gradient's formation involves the nuclear import of cytoplasmic Dorsal in response to an extracellular signal. Now, Robert DeLotto and colleagues report that the maintenance of the gradient is actually a dynamic process that also involves the Exportin 1-mediated nuclear export of Dorsal (see p. 4233). Using real-time, live imaging of embryos that express a Dorsal-GFP fusion protein,the researchers show that nuclear Dorsal concentrations change continuously during interphase and that the Dorsal gradient breaks down and reforms with every mitotic division. Dorsal, they report, constantly shuttles in and out of the nuclei during interphase. Furthermore, its diffusion is partly constrained to cytoplasmic domains around each syncitial nucleus. The researchers propose,therefore, that the generation and maintenance of the Dorsal gradient during fly embryogenesis involves both restricted long-range diffusion and the regulated nucleocytoplasmic shuttling of Dorsal.