A battery of nine lectins was applied to routinely processed endometrial biopsies to evaluate changes in glycoconjugate expression during the menstrual cycle and early gestation. Specific staining patterns emerged for glands, surface epithelium, predecidual and decidual cells, stromal granulocytes, and endothelium. Three lectins--wheat germ agglutinin (WGA), Ricinus communis-I (RCA-I), and Concanavalin ensiformis (Con-A)--showed consistent binding to epithelial and stromal cells in the menstrual cycle. WGA and RCA were bound to gland secretions whereas Con-A labeled epithelial cytoplasm. These three lectins stained occasional stromal cells early in the cycle, but WGA and RCA marked granulocytes whereas Con-A labeled predecidua in the late secretory phase. Succinylated WGA had a distribution similar to WGA but lacked its consistency and intensity. In the menstrual cycle peanut agglutinin reacted with ciliated cells. In addition, this lectin along with soybean agglutinin and Dolichos biflorus labeled gland secretions in pregnancy. The remaining lectins, Phaseolus vulgaris leucoagglutin and Ulex europaeus, marked some components, especially endothelium, but generally had less reactivity than the other lectins did. The results indicate that glycoconjugate production is correlated with the functional status of the endometrium. Presumably these glycoconjugates play a role in endometrial development necessary for nidation, and alterations in lectin distribution may reflect functional abnormalities not apparent by light microscopic study.