Adult male laboratory animals, including 38 mice, 17 rabbits and 8 rats, were dividedinto the experimental and control groups. The control animals were fed with a basic diet,and the experimental animals were fed with the same diet with 1% of condensed leci-thin in addition. They were maintained on the same diet for various periods (mice for10 weeks, rabbits for more than one year, and rats for 25 weeks) and were sacrificed forvarious cytological studies. The following techniques were adopted for the study of adrenal cortex: 1) Regaud'sfixing and Altmann-Cowdry's staining methods for mitochondria; 2) Ma's modificationof Kopsch-Kolatchev's method for Golgi apparatus; 3) Carnoy's fixing and Kurnick'sstaining methods for nucleic acids; 4) Carnoy's fixing and hematoxylin-eosin or Mallory'sstaining methods for general morphology; and 5) frozen sections for measuring the nu-clear size. The animals fed with lecithin showed an increase in number and size of mitochon-dria in the adrenal cortical cells. The Golgi apparatus of these cells, as compared withthose of the controls, possessed a more complex network of thicker strands and showeda wider distribution both in the individual cells and through the entire cortex. Thelipoid vacuoles, the nuclear size, and the number of the nucleoli were also increasedslightly in these cells in the experimental animals. In spite of some individual varia-tions, the above changes indicated that the fundamental structures of the adrenal corticalcells were strengthened by feeding the animals with lecithin. The appearance of Golgi apparatus and lipoid substance in the cortical cells andtheir relation to the mitochondria were discussed. The reticular zone of the adrenalcortex is considered as a stratum of very active cells.