The bulge contains the most chemically evolved old stellar population in the Milky Way .
Thanks to microlensing , it is now possible to obtain high resolution echelle spectra of bulge stars near the main sequence turn-off , and study the abundance of elements that are affected by stellar evolution , such as lithium .
We have observed with the HIRES spectrograph on the Keck I 10m telescope the source star of the MACHO microlensing event 97BLG45 while it was magnified by \sim 1 magnitude .
Here we report the detection of the Li I line at \lambda 6707.8 Å in the echelle spectrum of this star , and measure the bulge lithium abundance for the first time : A ( Li ) = 2.25 \pm 0.25 .