The neuronal cell adhesion molecule axonin‐1 is composed of six immunoglobulin and four fibronectin type III domains. Axonin‐1 promotes neurite outgrowth, when presented as a substratum for neurons in vitro, via a neuronal receptor that has been identified as the neuron‐glia cell adhesion molecule, NgCAM, based on the blocking effect of polyclonal antibodies directed to NgCAM. Here we report the identification of axonin‐1 domains involved in NgCAM binding. NgCAM‐conjugated microspheres were tested for binding to COS cells expressing domain deletion mutants of axonin‐1. In addition, monoclonal antibodies directed to axonin‐1 were assessed for their ability to block the axonin‐1‐NgCAM interaction, and their epitopes were mapped using the domain deletion mutants. The results suggest that the four amino‐terminal immunoglobulin domains of axonin‐1 form a domain conglomerate which is necessary and sufficient for NgCAM binding. Surprisingly, NgCAM binding to membrane‐bound axonin‐1 was increased strongly by deletion of the fifth or sixth immunoglobulin domains of axonin‐1. Based on these results and on negative staining electron microscopy, we propose a horseshoe‐shaped domain arrangement of axonin‐1 that obscures the NgCAM binding site. Neurite outgrowth studies with truncated forms of axonin‐1 show that axonin‐1 is a neurite outgrowth‐promoting substratum in the absence of the NgCAM binding site.