Previously designed stereological method for estimating axial ratios (X0/Y0) of microvessels (MVs) whose shape is approximated by elliptical cylinders was applied for analysis in the rat thyroid perifollicular hemocapillaries in hypercalcemia (Ca gluconate--10% i.m., 0.7 ml/day, for 3 days). Electron microscopy revealed the size of major (X) and minor (Y) radii of ectioning profiles of the capillaries. The X/Y distribution corresponded to use of characteristics foe elliptical cylinder model's stochastically geometric 3D/2D relation of distribution of two--or three-dimensional (3D), and observed, or two-dimensional (2D), axial ratio values. The X0/Y0 values of the MVs under study were estimated as X0/Y0 approximately 1.3 for 79% and X0/Y0 approximately 2.7 for 21% of capillaries. The estimates obtained are of comparable value with the X0/Y0 calculated previously for the thyroid capillaries of the normal rat. They can be employed in physiological studies of the MVs.