Discerning mechanisms underlying plasticity. Progress in the field of bone marrow stem cell plasticity must be made on multiple fronts simultaneously. To discern the mechanisms underlying plasticity, we must optimize and standardize the experimental approaches used so that the data obtained are as reproducible and definitive as possible. While making progress in our understanding of the underlying mechanisms, however, we must not lose sight of the potential therapeutic applications of these findings. By assessing the potential clinical benefits of stem cell administration in different disease models, we will gain insight not only into their therapeutic potential but also into the mechanisms by which plasticity occurs.