Diagnostic and therapeutic technology continues to advance rapidly, as does our knowledge of therapeutics and of clinical research methods. Unfortunately, these advances have been only poorly coupled with our knowledge of therapeutic principles, leading to increasing uncertainty about which technologies are truly effective and, amongst those that are effective, which are most effective for the cost. This article presents general principles derived from several investigators' experiences with clinical trials, and uses them to suggest how future clinical trials may differ from current approaches. A proposed organization for future trials also is elucidated.