The human uterine epithelium has been studied by means of mild (0.1, 0.01% respectively) periodic acid (PA) oxidation followed by thiosemicarbazide-silver proteinate staining. Distribution of silver deposits provided evidence for glycoconjugates and was in the case of oxidation with 0.01% PA selective for sialic acid (N-acetylneuraminic acid) complexes. The electron dense silver particles were detectable at the outer side of apical plasma membranes and on the inner surface of lysosomal membranes. Also the marginal zone of lipid droplets reacted regularly. Since the lower concentration of PA proves sialogycoconjugates selectively, the positive staining depicted not only those in the membrane compartments but also as a layer between the hydrophobic content and the hydrophilic cytoplasm. In the granular endoplasmic reticulum of the individual microvillous cells a special glycoprotein of paracrystalline organisation was detected. The functional significance of this substance remains unclear. Nuclear channel systems (NCS) are frequently observed in the epithelial cells in the uterine glands. Similar staining properties of the NCS and nuclear envelope support the hypothesis of its nuclear origin.