The ultrastructural features of the ectal mandibular glands of the paper wasp Polistes versicolor are described. These glands contained a secretory portion and a sac-shaped reservoir. Muscle fibers were observed around the secretory cells close to where slender ducts arose to reach the reservoir sac. These fibers were probably involved in the release of secretion. The early secretory cells contained rough endoplasmic reticulum and Golgi complex with varying features, as well as the mitochondria necessary to sustain the energy requirements for the secretory activity. Smooth endoplasmic reticulum appeared only during the late stages of the secretion cycle. Synthesis and secretion occurred simultaneously and continuously within each cell, with the secretory cycle being essentially asynchronous throughout the gland. The cells of the reservoir wall differed from those in other hymenopterans by their lack of a dense cuticle lining the lumen. These cells also produced lipids that probably will contribute to the ultimate composition of the secretion.