Porphyrinic sensors were used for the in situ monitoring of nitric oxide release and diffusion in the endothelial cell, as well as its subsequent diffusion from the endothelial cell through the muscle cells found in the rabbit aorta. The experimental data was compared with that predicted based on Fick's equation for linear diffusion. A time delay of 1.5 s between prediction and experimental concentration of NO due to its chemical reactions was observed at the distance of 100 microns from endothelial cell. About 37% of the NO produced is consumed in chemical reactions in the aorta.