The ultrastructure of rat myometrium was studied to determine the types and relative number of cell-to-cell contacts between smooth muscle cells after various hormonal treatments. Intermediate and close contacts were present between cells of the longitudinal and circular muscle layers. No nexuses were present between smooth muscle cells but nexuses were consistently found between fibrocytes surrounding bundles of smooth muscle cells. More intermediate contacts were present in the longitudinal muscle layer than the circular muscle. Close contacts were not appreciably affected by hormonal treatment. More intermediate contacts were found in tissues from pregnant or estrogen-treated animals than from estrogen-progesterone-treated animals. The mechanisms for electrical coupling between uterine muscle cells are discussed in light of these findings.