AbstractUsing the Falck‐Hillarp method for demonstration of biogenic amines, the presence of indole alkylamine (possibly 5‐hydroxytryptamine) containing enterochromaffin cells in strongly ciliated areas of the lancelet intestine was confirmed. An electron microscopic investigation of these areas, i.e. the “lateral ciliated tract” and the “dorsal ciliated tract”, revealed two cell types. 1. Mucous cells, equipped with tall cilia and giant rootlets, constitute the dominating type. 2. Enterochromaffin cells, containing numerous electron dense granules, are sparsely scattered among the mucous cells. The intestinal indole alkylamine is believed to be involved in the regulation of cilia