The discovery that bile canaliculi are capable of spontaneous contractile activity has led to their use in the investigation of the physiology of the liver cell. The contraction of a bile canaliculus is dependent on the network of actin, which is found in the pericanalicular region of the hepatocyte, and agents that inhibit actin filaments interfere with canalicular contraction. Injection of calcium directly into the cytoplasm of one hepatocyte of a cell pair results in contraction. Injection of calcium directly into the cytoplasm of one hepatocyte of a cell pair results in contraction of the canaliculus. To determine whether the contractile activity of adjacent bile canaliculi was coordinated, calcium was injected into one cell of a group of three hepatocytes that formed two neighboring bile canaliculi. Calcium microinjection resulted in contraction of the bile canaliculus contiguous with the microinjected cell and was followed by a contraction of the second, adjacent canaliculus. These secondary contractions occurred after an interval of approximately 45 seconds. The finding that bile canalicular contractions are coordinated with contractions occurring in a sequential fashion supports the hypothesis that, within the liver lobule, transport of bile within the canalicular network results from the coordinated contractions of the canaliculi.