[en] A study was performed on rats to verify the effects of ionizing radiation on the structure of the parotid glands of young rats. Thirty twenty five-day old rats (Holtzman) were equally distributed into two experimental groups: Group 1 - irradiated; Group II - control. Using a conventional X-ray apparatus, the region of the parotid glands was irradiated with a dose of 300 R, this procedure was repeated every 48 hours up to an exposition of 1200 R. After periods of 3, 8, 13, 18, and 28 days, the animals belonging to both groups were sacrificed and the parotid glands removed and fixed in 10% formalin and Bouin liquid for 24 hours. The sections were stained by hematoxylin and eosin and Mallory's Thricromic, allowing analysis through the usual optical microscope. The following conclusions may be drawn through the methodology used: the Group 1 - rats gained body weight uniformly after the 13 sup(th) day, although this was not equivalent to the control group; the critical phase of glandular disorganization determined by irradiation corresponded to the experimental period of 8 days, decreasing in the subsequent days; the serous acini and the striated ducts showed to be more radium sensitive even under the use of low fractionated doses; the parotid glands showed indications of gradual morphological recovery after the last exposition to X-rays. (author)