Living hepatocytes observed under standard methods of cell isolation and culture show frequent active contractions of bile canaliculi when viewed by time-lapse cinephotomicrography. This report gives details of the methods used to show the contractions. In addition, the characteristics of the contraction pattern are defined and analyzed. The contractions are regular, canalicular contraction time (systole) lasts 60 sec, and the most probably interval between contractions is 5 1/2 min. The finding of a regular pattern of contraction suggests an ordered, programmed, and integrated mechanism which entails a high degree of communication and functional coordination between neighboring hepatocytes.