We evaluated gallbladder contractility in 58 colicky infants and 57 age-matched controls. Gallbladder size was measured before and 1 h after feeding and the contraction index of the gallbladder was calculated. The results showed decreased contractility of the gallbladder in colicky infants: mean contraction index in colicky infants was 56% (95% confidence interval, 49-63%) and in controls 67% (61-73%). No difference was found in the fasting size of the gallbladder. Postprandial contraction was decreased in colicky infants examined in the evening (n = 14) compared with those examined in the morning (n = 44). Decreased contraction of the gallbladder was found in those colicky infants who presented colicky cry compared with colicky infants without symptoms at the time of examination. No structural abnormalities were found in the general abdominal survey. In conclusion, infants with colic have hypocontractility of the gallbladder. This indicates abnormal biliary tract physiology in association with infantile colic.