This study reports the ultrastructural cell modifications in the myoepithelium of the Harderian gland during the postnatal development of the Syrian hamster. Tissues were obtained from male and female hamsters at days 1, 3, 5, 7, 10, 12, 15, 17, 20, 27, 37, 46 and 90 after birth, and processed for transmission electron microscopy. Electron microscopy was coupled with point counting methods to quantitate changes in several subcellular organelles during the course of myoepithelial cell maturation. The myoepithelial cells in this gland remained immature at birth. The earliest age of development when organized bundles of microfilaments were observed was 7 days. By the 12th day, the myoepithelial cells had developed most of their specific characteristics and resembled the mature form. Myoepithelial cells mature synchronously with each other and with the secretory cells. No undifferentiated myoepithelial and myoepithelial cells, the secretory endpieces of the adult hamster Harderian gland contain a third cell type which resembles the myoepithelial cell in shape and has an extremely electron-lucent cytoplasm lacking microfilament bundles.