The ciliated band of the Strongylocentrotus purpuratus embryo consists of a columnar epithelium, 3-5 cells wide, which gives rise to a small number of neuroblasts. It arises late in development, as a border separating the squamous epithelial cells of the oral and aboral ectoderm. To determine the lineage origins of this structure, we performed double labeling experiments at the 2-cell stage and the 16-cell stage, which were designed to reveal clonal boundaries in the ciliated band. The ciliated band forms in a region of the ectoderm derived from descendants of the following blastomeres: No, VO, Na1u, Na2u, right and left NL1u, and right and left NL2u. In contrast to the lineage contributions of the embryonic territories established early in development, lineage origins of the ciliated band are variable. Specification of the ciliated band thus depends on intercellular interaction rather than lineage.