- If psychoanalytic treatment is to survive in the era of evidence-based medicine and managed care systems, empirical evidence is needed to demonstrate its unique nature and effectiveness. To address this need, comprehensive analyses were conducted of data from the Menninger Psychotherapy Research Project (Wallerstein 1986). These analyses addressed three questions: (1) What are the differences in outcome between psychoanalysis (PSA) and supportive-expressive psychotherapy (SEP)? (2) With what types of patient, and in what ways, are these two psychodynamic treatments differentially effective? (3) Are these differences in outcome the consequence of possibly different mechanisms of therapeutic action? PSA was found to contribute significantly to the development of adaptive interpersonal capacities and to the reduction of maladaptive interpersonal tendencies, especially with more ruminative, self-reflective, introjective patients, possibly by extending their associative capacities. SEP, by contrast, was effective only in reducing maladaptive interpersonal tendencies and only with dependent, unreflective, more affectively labile anaclitic patients, possibly by containing or limiting their associative capacities.