Arginine vasopressin (AVP) is often expressed in small cell lung cancer (SCLC), and a 65-bp AVP minimal promoter fragment is sufficient to restrict activity to SCLC in vitro. We now describe a motif with homology to the neuron-restrictive silencer element (NRSE) within this fragment. Electrophoretic mobility shift analysis demonstrated that multiple specific complexes are bound by this motif. These complexes are cross-competed with a characterized SCG10 NRSE probe and do not bind to the AVP probe with a specific mutation in the NRSE. The complexes vary in mobility between lung tumor cell lines, showing different levels of AVP expression, and some are differentially bound in SCLC. Overexpression of a neuron-restrictive silencer factor expression construct can silence reporter gene expression supported by the AVP promoter in SCLC, although this was dependent on both the level of endogenous AVP expression in the cells and putative enhancer elements in larger promoter constructs. Activation of the proximal AVP promoter in SCLC is therefore proposed to, at least partially, rely on modulation of normal repressor activity at the NRSE.