In the intestinal mesentery of 40 white rats and 40 mongrel dogs by means of azure-eosin staining, silver impregnation, vital microscopy and certain histological methods, after left-sided cervical vagotomy it has been demonstrated that an increasing functional activity of mast cells is reached by: 1. increasing number of the mast cells; 2. increasing part of degenerating forms; 3. elevating part of the most active forms. As to the microcirculatory bed, a decreasing volume is observed at the expense of opening the arteriolo-venular anastomoses, a certain spasm of the microvessels and loosing of the capillary network. In the intervascular connective tissue, destabilization of the connective tissue elements is observed. Biomicroscopy reveals an accelerated time for the blood elements to get out of the vascular bed. The data obtained demonstrate that the postvagotomic reaction of the microcirculatory bed and its mast cell apparatus is limited with the innervation zone of the vagus nerve.