Secretory epithelium in venom glands of specimens of Centruroides vittatus (Say) from Texas and the dangerously venomous Centruroides limpidus tecomanus Hoffman from Colima, México, was examined by light and electron microscopy. In both species the glandular epithelium was thrown into numerous ridges, folds, and irregular finger-like processes. The luminal surface of the epithelium was marked by the presence of closely spaced microvilli, a finding not previously noted. Three types of granule-containing cells, classified by granule size, were present. These granules, fine, medium, and large, stained dark blue with metachromatic dyes in material prepared for light microscopy. Each cell contained granules of only one size. We assumed that the granules were venom particles. Two types of mucus-containing cell were interspersed among the venom cells. In one type the contents were amorphous; in the other the mucus was contained in globules of various sizes and had either a linear or dotted appearance. Contents of these cells stained pink with toluidine blue. The secretory process was apocrine in these species. Although the species studied differ greatly in their toxicity for man, no differences in the morphology of their venom glands were found by light and electron microscopy.