In suckled rats, neurosecretory bursts of two oxytocin cells located in two different magnocellular nuclei were almost simultaneous before each milk ejection. The time elapsing between the onset of two corresponding neurosecretory bursts varied in duration (from 0 to 368 ms) and in order from one pair of cells to another, from one pair of bursts to another for successive bursts of a given pair of cells and independently of whether one of the two cells belonged to the paraventricular or supraoptic nuclei. However, the neurosecretory burst with the highest amplitude began before the other corresponding burst in most cases. Possible inter- and intranuclear synchronization mechanisms are discussed.