OBJECTIVES:Childhood abuse is a powerful prognostic indicator in adults with major depressive disorder (MDD) and is associated with numerous biological risk factors for depression. The purpose of this investigation was to explore if antidepressant medication affinity for the serotonin transporter moderates the association between childhood abuse and treatment response. METHODS:Our sample included 52 outpatients with MDD who had received up to 26 weeks of pharmacotherapy, stratifying antidepressant medications with a high versus a low affinity for the serotonin transporter. Patients completed the Hamilton Rating Scale for Depression, Beck Depression Inventory II, Home Environment Questionnaire, and Ontario Health Supplement: Child Abuse and Trauma Scale to assess depression and childhood abuse. RESULTS:Medication class moderated the link between 3 indices of childhood abuse and treatment response such that higher levels of childhood abuse were associated with higher levels of depression severity after treatment only in those patients receiving antidepressant medications with a weak affinity for the serotonin transporter. CONCLUSIONS:This pilot study suggested that prolonged exposure to stress during childhood may result in biological vulnerabilities for depression, which may in turn be differentially targeted by pharmacological agents which target serotonin to a greater or lesser degree.