To investigate the age-related changes in the acceptance of a protein hydrolysate formula, Nutramigen, and to determine whether infants' response to a novel formula is related to their mothers' willingness to try novel foods, healthy infants, who were either 1 to 2 (Group 1) or 7 to 8 (Group 1 retested and Group 2) months of age, were fed their familiar brand of milk- or soy-based formula on one testing day and a casein hydrolysate formula, Nutramigen, on another. The data revealed that infants younger than 2 months detected the difference between Nutramigen and their regular formulas as evidenced by a slight, relative depression in intakes (p = .04). However, these infants drank substantial amounts of the Nutramigen and satiated while feeding it. In marked contrast, virtually all of the 7- to 8-month-old infants rejected the Nutramigen (p = .000002), and this was evident within the 1st minute of the feed. Finally, there was a significant correlation between the mothers' eating habits as determined by the questionnaires and the 1- to 2-month-old infants' response to Nutramigen. Mothers who exhibited a greater willingness to consume novel foods (p = .003) or less food neophobia (p = .04) had infants who consumed relatively more of the Nutramigen.