The structure of the alimentary tract of the third stage infective larva of Nippostrongylus brasiliensis has been described. The cuticle which lines the buccal cavity and oesophagus differs from that which lines the mouth and covers the external surface of the nematode. The oesophagus is a cellular structure and is not, as previously thought, a syncytium. The secretory granules of the oesophageal glands are surrounded by multi-layered membranes which give a myelinated appearance to the granules. The cells of the oesophago-intestinal junction are lined with cuticle and are presumably part of the stomodaeum. The intestine is thin-walled and the cells bear short, widely spaced microvilli. The lumen of the intestine contains whorls of membranes which are probably phospholipid and could act as a food reserve for the larva. The rectum and anus are lined with cuticle.