Gap junctions are channels made up of connexin (Cx) proteins that allow direct communication between adjacent cells. The number of Cx43 junctions rises dramatically in the myometrium of the uterus prior to labour, which could help synchronize uterine contractions during delivery by increasing smooth muscle cell coupling. Until now there has been little firm evidence to support this idea. On p. 1715, however, Klaus Willecke and co-workers use a sophisticated conditional-knockout approach to demonstrate the importance of Cx43 for a successful delivery. They have generated mice in which they can abolish expression of Cx43 specifically in smooth muscle by treating them with tamoxifen. The authors find that, under these conditions, parturition still occurs but is often significantly delayed. In addition, they use dye-coupling assays to show that primary myocytes from the animals exhibit decreased cell-cell coupling whereas other features of the cells are unaffected. Their findings thus not only define the critical role of Cx43 in the myometrium in vivo for the first time but also underscore the importance of gap junctions for smooth muscle cell function.