RBC deformability and PMN-endothelial interaction have been used as two examples to illustrate how recent investigations have generated information from molecules to micromechanics and the microcirculation, and how some of the results can be used to understand the physiology and pathophysiology in man. While this presentation on the molecular basis of microcirculatory events is focused on micromechanics, active work is being conducted to establish the molecular basis of many other microcirculatory processes. These include endothelial transport, vascular smooth muscle activity, neurohumoral control of the microcirculation, and angiogenesis, as well as some of the disease states such as ischemia, shock, and cancer. The field is still in its infancy, and we are only seeing the tip of the iceberg. Further developments in this fertile interdisciplinary field will allow us to gain further understanding of the molecular basis of the microcirculatory processes in health and disease. CONCLUSIONS (i) The deformability and interactions of blood cells play a significant role in microcirculatory dynamics. (ii) Modern biological approaches have provided insights into the molecular bases of blood cell deformability and interactions. (iii) Understanding of the physiology and pathophysiology of the microcirculation requires the application of knowledge derived from molecular and cell biological studies to the in vivo microcirculatory preparations. (iv) Bridging of the new biology and in vivo microcirculatory investigations represents a great challenge and a golden opportunity for microcirculation researchers.