The abundance of lithium in stellar atmospheres presents an important observational constraint to the hydrodynamical models of the outer layers of stars. It can be considered as a cumulative measure of the extent of matter exchange between surface and deeper layers during the stellar evolution.

From the observed large scatter of lithium abundances in evolved stars it follows that the efficiency of mixing has been highly variable from one object to another. At present, it seems to be difficult to find any satisfactory explanation to the lithium abundances of individual stars. We suppose that at this stage the statistics of lithium abundances in different types of stars can give some insight into the character of mixing processes operating in stars. In this report some observational results about the distribution of the lithium abundances in normal late-type giants are presented.