Approximately 25% of infants with moderate or severe colic (crying > 3 h d(-1)) have a cow's milk-dependent colic. The author recommends a strict cow's milk-free diet for the mother (with an extra supplement of calcium) in breastfed infants and a casein-hydrolysate formula for formula-fed infants. With this dietary regimen, there will be no nutritional problems. Later in infancy a relatively high proportion of the infants will continue to show an adverse reaction to cow's milk and will also develop allergies to other foods. Several signs (e.g. increased macromolecular absorption, increased motilin levels in serum, increased breath hydrogen excretion, decreased gallbladder contractility) indicate an abnormal intestinal function in colicky infants. The nature of this abnormality is still unknown.