In response to concerns about inappropriate testing and healthcare costs, clinicians and laboratorians should work together to evaluate laboratory tests. Studies of routine laboratory tests ordered for screening and case-finding in the preoperative setting, at hospital admission, and in the ambulatory setting have not provided sufficient evidence of the benefits of case-finding when evaluated against commonly used criteria for screening procedures. We adapt a conceptual framework developed from radiology for evaluating imaging technologies to evaluate laboratory tests. The framework addresses diagnostic efficacy (whether the test correctly identifies abnormalities), diagnostic effectiveness (whether the test changes the physician's diagnoses), therapeutic efficacy (whether the test changes patient management), and therapeutic effectiveness (whether the test changes patients' outcomes). We propose that clinicians and laboratorians use this framework to evaluate the diagnostic efficacy, diagnostic effectiveness, therapeutic efficacy, and therapeutic effectiveness of laboratory tests in the ambulatory setting and in other settings.