Well-conducted surveys can clarify unmet clinical need and explore many unresolved scientific issues. Surveys can generate hypotheses about the biologic underpinnings of the symptom, characterize fatigue syndromes in different populations of medically ill patients, and clarify the relationships among fatigue characteristics and various etiologies or comorbidities. The relationships between fatigue qualities (possible subtypes) and demographic, disease-related or treatment-related variables, and objective indicators of disease (e.g. specific metabolic disturbances such as cytokine levels) can be illuminated by this research. Surveys also can potentially clarify responses to therapy and guide the development of subsequent trials. For example, evaluation of a range of responses following treatment with epoetin alfa might be able to infer a direct cognitive response consistent with new information about the presence of erythropoietin receptors in brain (Brines et al., 2000). If so, this would affirm the value of a trial in fatigued patients without significant anemia.