Carnitine acetyltransferase and palmitoyltransferase activity in the mucosa of the small intestine of rats rises after birth and falls at the time of weaning. The carnitine contents of the mucosa (free, acetyl-, palmitoyl- and total) decrease postnatally, reaching adult levels at the time of weaning. Orally administered 14C-carnitine is only slowly absorbed so that radioactivity is still high in plasma and organs 6 h later, whereas label given subcutaneously disappears from the plasma and tissues more rapidly. The intestinal mucosa also takes up carnitine from 14C-carnitine administered subcutaneously. It is concluded that carnitine plays an important role in the gut of suckling rats.