This article describes a new extracellular domain--AMOP, for adhesion-associated domain in MUC4 and other proteins. This domain occurs in putative cell adhesion molecules and in some splice variants of MUC4. MUC4 splice variants are overexpressed in several tumours; in particular, they are highly expressed in pancreatic carcinomas but not in normal pancreas. The presence of AMOP in cell adhesion molecules could be indicative of a role for this domain in adhesion.