IAfter the announcement of the discovery of the human genome in 2000, the focus of research in the field of medicine directed towards the assignement of physiological role of genes and their products. The number of genes and the number of possible interactions between proteins, gene products, make this effort a complex endeavour. Thus it is not easy to assign a function of a particular gene in normal and pathological conditions in a single cell, since cells are typically small and therefore difficult preparations for experimental manipulation. The research aims of our laboratory are focused on studies to reveal the function of single cells. In particular, we are studying the mechanism of fusion of the vesicle membrane with the plasma membrane. The mechanism of vesicular trafficking is a universal characteristic of all eukaryotic cells, but still poorly understood. In the last five years a series of experiments was conducted on a number of cell types to test the hypothesis proposed in the past, that the mechanism of vesicle fusion is organized in a sequential scheme. The results obtained in our studies are in support of a mechanism of vesicular fusion in which multiple functional modules of fusion between the vesicle and the plasma membrane exist in a cell. The existence of such multiple functional modules enables differential secretion of vesicle content from vesicles containing different cargo in different vesicles within a cell. This direction of research (molecular cell physiology) is also recognized as physiological-functional genetics. Studies at the level of single cells are imperative, since cells constitute building blocks of the organism and are therefore elements of physiological and pathological processes. Therefore to understand pathobiology and the role of specific genes in these processes it is essential to conduct research on single cells. Progress in this field is also determined by the available technologies and the development of new approches, which are typically demanding, integrating knowledge from different disciplines (electronics, computing, optics, phzsics, micromechanichs,etc.), and therefore less appealing in comparison to main stream biochemistry and molecular biology, which represent the most popular strategies in biomedicine at this momement. However cell sciences represent an element of competitive advantage.