Two hundred and nineteen infants, consecutively born, took part in a prospective study of infantile colic from birth to 12 weeks of age. The prevalence of infantile colic in this group was 17.4%. S-motilin was studied in 78 term infants (19 with and 59 without infantile colic) at birth (cord blood), at one day, and at 6 and 12 weeks of age, respectively. Basal motilin levels were raised both in cord blood (p less than 0.01) and in blood from neonates (p less than 0.001) who developed colic as well as in 6 week (p less than 0.05) and in 12-week-old infants with colic (p less than 0.01). Formula-fed infants with colic had higher basal motilin levels than formula-fed controls at 6 and 12 weeks of age (p less than 0.05). Breast-fed infants with colic had higher basal motilin levels than breast-fed controls at 12 weeks of age (p less than 0.05). The raised levels of motilin from the first day of life in infants who develop infantile colic might indicate that the gastrointestinal tract is affected in infants with infantile colic, before any symptoms of colic appear.