The Harderian glands of male Albino rats 1-24 months of age were studied by electron microscopy. In most glands, a few acinar cells contained straight and curved trilaminar profiles identical in form to the material in the luminal masses of porphyrin pigment. They resembled the structures which several investigators have identified as crystals of protoporphyrin IX in porphyric human and mouse hepatocytes. Protoporphyrin IX is the predominant form synthesized by rat Harderian cells in vitro. The trilaminar profiles were within the cytoplasm but not within the lipid secretory vacuoles. A large number of the acinar cells had finely tubular endoplasmic reticulum (ER). However, cells containing the trilaminar forms consistently had dilated ER vesicles. This change may have been a prelude to cell death, for some pigment-containing cells attached to the acinar basal lamina also displayed fragmented organelles and a loss of density of the cytoplasmic matrix. In some acinar lumina there was abundant cell debris along with the trilaminar profiles. It is concluded that in the rat, some of the Harderian free porphyrins can be released through cell death.