Résumé
We study the formation of Li lines in a case study of an S-type AGB star in the SMC. AGB stars may be important providers of$^7$ Li to the interstellar medium. Abundance analysis of these stars is difficult due to the heavy molecular blanketing, uncertainties in the model atmospheres and possible departures from LTE in the Li atomic level populations. We address here the latter problem and somewhat also that of background molecular line formation. We do not find non-LTE effects big enough to alone rule out the possibility that the reported super-Li-rich stars exist. There are, however, several other complications connected to the formation of the Li lines in these stars.