Sixth Annual Graduate Hospital Research Symposium REGULATION OF SMOOTH MUSCLE PROGRESS IN SOLVING THE PUZZLE Every so often a scientific conference comes at a time when everyone has new and exciting information, when old "dogmas" do not seem to be as well established, and when speakers and participants alike are ready to challenge interpretations of old and new experimental data. This was such a conference. What turns on a smooth muscle cell? The precise answer to this question has eluded scientists for much longer than I have been involved in the field. We know that an increase in cytosolic calcium is necessary and we know that phosphorylation of the 20 kDa myosin light chain is an important step in the process. We do not know if other processes are necessary for the initiation and lor maintenance of a smooth muscle contraction nor do we know if other processes modulate the regulation of contraction. The goal of the symposium on which this volume is based was to explore the most current hypotheses for the answers to these questions. I believe that after reading the chapters included in this volume, you will agree that this goal was achieved. The importance of calcium and calmodulin dependent myosin light chain phosphoryla­ tion in the regulation of smooth muscle contraction was reinforced by many presentations. However, the status of myosin light chain phosphorylation as a simple calcium dependent switch came under serious suspicion.