Nineteen patients with previously untreated invasive squamous cell carcinoma of the uterine cervix were treated by irradiation alone at the Keimyung University Hospital from January, 1990 to July, 1991. The serial samplings of the tissue taken before and during radiation of the uterine cervix were studied by light and electron microscopic examination. Radiation-induced cellular changes, particularly nuclear degeneration was pronounced. The tumor invasion pattern remained unchanged but the number of mitosis and tumor cells decreased, The number of infiltrating inflammatory cells, multinucleated giant cells and karyolytic cells were increased with radiation. Fibrosis was also increased. Electron microscopically, the amount of tonofilament in the tissue samplings was increased in the postirradiated state, but the desmosomes were decreased in numbers. Fibroblasts began to appear after an irradiation dose of 2700 cGy. After an irradiation dose of 3000 cGy or more, tumor cells were nearly completely degenerated and displaced with mature fibrotic tissue. There was an increase of activated fibroblasts and collagen fibers but a decrease of inflammatory cells in the interstitial tissue. Swelling of the mitochondria and endoplasmic reticulum, loss of intercellular bridges and an increased number of secondary lysosomes were also found with radiation.