The endothelium is a complex network of cells that lines the entire vasculature and controls virtually all cardiovascular functions. Changes in the behaviour of endothelial cells underlies almost all cardiovascular disease. To regulate cardiovascular function, the endothelium integrates signals from hundreds of circulating factors and makes a determination about output. The endothelium is responsive to hundreds of circulating factors but how, as a whole, it detects and interprets these signals is not precisely understood. Signals arrive from as close as neighbouring cells to those from the most remote outpost of the body and provide endless streams of instructions to the endothelium. How the endothelium decodes the cacophony of chemical information is not understood and was studied by examining the individual behaviour of thousands endothelial cells. Male Sprague Dawley rats (250-300g) were euthanized by CO2 overdose. Second order mesenteric arteries were extracted, cut open and the endothelium loaded with a Ca2+ indicator, Cal-520/AM. Endothelial Ca2+ signalling was imaged in thousands of cells by fluorescence microscopy and cells individually analysed using custom-written software. To assess how information was integrated in the endothelium, the Ca2+ responses to four different agonists (ACh, ADP, ATP and Histamine) was studied. Significantly, the results show that the cells most sensitive to each agonist were spatially distinct (unique). These results suggest that agonist-specific sensory cells are distributed throughout the endothelium. To further test this hypothesis, we carried out full concentration response experiments to identify the concentration at which 25% of cells responded to each agonist. Next we applied the EC25 concentrations of each agonist to the same artery. Interestingly, when 25% (EC25) of cells were activated by ACh there was no substantial cross-over of the 25% of cells that were activated by histamine (only 13 ± 4.3% of activated cells responded to both agonists, P<0.05). The same was true for ACh vs ATP (11 ± 3.6%) and ACh vs ADP (14.5 ± 3.2%). Interestingly, even with ATP and ADP there was only a 49.6 ± 5.6 % cross-over between the cells that responded to the EC25 of each agonist. The higher value probably arose due to the various purinergic receptors that are present on the endothelium. Our findings suggest the endothelium is a complex network and distributed sensory system that successfully detects a multitude of activators by utilising spatially distinct cells that have a high affinity for a specific agonist. These features enable the endothelium to detect simultaneously arriving stimuli and carry out several functions in parallel. For example, if only 25% of the cells are responding to an agonist then the remaining 75% can respond to a completely different stimulus. Furthermore, the cross-over between two agonists is ~10% of all activated cells.