A study evaluating the treatment of colic by modification of the parent-infant interaction was carried out in a private practice setting. The study population consisted of 30 normal colicky infants and 30 control infants matched for age in weeks, sex, and the presence of siblings. The two groups were similar with regard to sociodemographic and other variables with the exception that mothers of colicky infants were older (P less than .005). Quantitative measurements of crying were obtained using prospective diaries of infant behavior. Colicky infants were found to cry 2.6 +/- 1.1 h/d as compared with 1.0 +/- 0.5 h/d for control infants (P less than .001). The treatment of these infants was based on the assumption that colic results from inappropriate parental responses to the baby's crying and consisted of counseling the parent on more effective responses. This resulted in the infants' crying decreasing from 2.6 +/- 1.1 h/d to 0.8 +/- 0.3 h/d (P less than .001), no different from the average of the control group. It is concluded that a major cause of colic is the misinterpretation of infant cries leading to ineffective responses, and that this can be managed by counseling parents on how to respond to infant crying.