Morphometrical analysis of microtubules (MT) and coated vesicles (CV) was done on electron micrographs of the murine mammary gland sections at the final stages of functional maturation of secretory cells (SC), as well as at different stages of the cell secretory cycle (CSC). The results obtained allow to make the following conclusions: 1) dynamics of changes in the MT count in different subplasmalemmal cell compartments is similar, being directly associated with heterochronical character of CSC processes; 2) the maximum MT count in SC was seen during formation of the secretion product, this increase occurring at the expense of short MT, which are disassembled before and during exocytosis of secretory vesicle (SV) contents; 3) changes in the number of MT and CV are of similar character, which was revealed by morphometrical analysis of SC in the course of maturation. The number of MT and CV in SC increased rapidly and significantly on the 1st and 2nd days after parturition, compared to that observed 1-2 days before parturition. However, the number of MT and CV decreased by the 10th day of lactation, when the mammary secretory activity reached its maximum. Both correlation and regression statistical analyses made during the CSC development point to a linear relation between MT (x) and CV (y) numbers. Regression of y on x is: y = -0.89 + 12.43x. A hypothesis about the possibility of MT participation in CV and SV transport and in the formation of a barrier on the path leading to exocytosis of SV contents is suggested.