A prospective, longitudinal design was used to determine the role of nonpharmacologic factors in the development of posttreatment nausea (PTN). Forty-five women with no previous chemotherapy experience who were receiving a single regimen of adjuvant chemotherapy for breast cancer were interviewed before and after their first six infusions. Seventy-one percent of patients developed PTN. The PTN was related to the following: patients' physical status at the onset of treatment; heightened anxiety during infusions; susceptibility to nausea and vomiting after eating certain foods; and expectations of developing chemotherapy-related nausea. Anxiety during infusions, susceptibility to nausea and vomiting, and expectations of side effects also accounted for differences in the frequency, intensity, and severity of PTN. These findings offer strong support for the view that nonpharmacologic factors contribute to individual differences in gastrointestinal responses to chemotherapy.