- Mental health services in Israel are about to undergo a major, and quite controversial, reform. Yet both those advocating these reforms and those opposing them refrain from resorting to empirical science in arguing their respec- tive cases. In the present article, we present findings concerning the central role of patients' individual differences in the outcome of mental health services. Data is presented from three research projects: 1. The National Institute of Mental Health (NIMH) Treatment of Depression Collaborative Research Program (TDCRP), in particular recent publications by Blatt, Zuroff, Shahar and their collaborators, 2. The Partnership Project in severe mental illness, and 3. The Menninger Psychotherapy Research Project (MPRP). Findings from these three projects, largely predicted by Blatt's theory of interpersonal relatedness and self-definition, suggest that an effective, evidence-based mental health practice is contingent upon practitioners' sensitivity to pretreatment patient characteristics. Clinical and policy impli- cations of this conclusion are discussed.