Biopsy specimens of the human vagina were studied by light and electron microscopy. In the nonpregnant state, the collagenous fibers were tight and regular. During pregnancy and after delivery the collagenous fibers were irregular and more spread out. Pronounced edema, increased vascularity, and dilated blood vessels were also characteristic findings; however, no interstitial hemorrhage or perivascular granulocyte infiltration was noted. At electron microscopy, collagenous fibers were thick and compact in the nonpregnant state, but thin fibrillar components with amorphous material were observed during pregnancy and post partum. Fibrillar elements were sparse around the fibroblasts and fat droplets in the fibroblasts were noted at term and after delivery. The possible involvement of prostaglandins released from fibroblasts and/or blood vessels is suggested in these processes.