In frequently occurring life-threatening diseases such as cancer, AIDS and cardiovascular disease, there is a need of significant public health importance for rapid yet reliable evaluation of promising new therapeutic interventions that might provide greater efficacy and reduced toxicity. Leadership from statistical scientists is essential to effectively address many of the challenges resulting from this need. By discussing recent experiences, primarily in the area of oncology and AIDS clinical trials, we will illustrate several of these challenges. We also will review some designs and methods that have been implemented in these settings. Particular attention will be given to experiences from involvement with FDA Advisory Committees and with Data Monitoring Committees for clinical trials sponsored by industry or by the National Institutes of Health. Among issues to be discussed will be the role of independent monitoring committees and group sequential guidelines in randomized clinical trials, the evaluation of equivalence trials and the use of surrogate and auxiliary endpoints.