Development, spreading and decay of the thermohaline properties of two Labrador Sea Water (LSW) classes are described. During the development phase, a specific LSW class repeatedly mixed by winter convection in the Labrador Sea becomes colder, denser, thicker and deeper. Once convection weakens, the LSW class becomes isolated from the upper layer and starts to decay, rapidly losing its volume while retaining the same density due to isopycnal mixing with the neighbouring warm saline intermediate waters. A similar pattern in temperature, salinity and density is seen in the other basins with different time lags from about two years in the Irminger Sea to ten years in the northern Iceland Basin and Rockall Trough regions. The influence of LSW on the thermohaline properties of other North Atlantic water masses is also discussed.