  The aim of this work is to use full evolutionary models to derive
observational constraints on the mass loss rate of the upper Asymptotic Giant
Branch (AGB) stars. The observations used to constrain the models are the
relative number of luminous Lithium rich AGBs in the Magellanic Clouds and the
s-process enhancement of the same sample. We find that we can put lower and
upper limits to the mass loss rate during the AGB phase. The mass loss
calibation obtained in this work implies that massive AGBs do not contribute
significantly to the lithium enrichment of the interstellar medium.
