  Aims. We seek to probe the Galactic bulge IMF starting from microlensing
observations. Methods. We analyse the recent results of the microlensing
campaigns carried out towards the Galactic bulge presented by the EROS, MACHO
and OGLE collaborations. In particular, we study the duration distribution of
the events. We assume a power law initial mass function, $\xi(\mu)\propto
\mu^{-\alpha}$, and we study the slope $\alpha$ both in the brown dwarf and in
the main sequence ranges. Moreover, we compare the observed and expected
optical depth profiles. Results. The values of the mass function slopes are
strongly driven by the observed timescales of the microlensing events. The
analysis of the MACHO data set gives, for the main sequence stars, $\alpha=1.7
\pm 0.5$, compatible with the result we obtain with the EROS and OGLE data
sets, and a similar, though less constrained slope for brown dwarfs. The lack
of short duration events in both EROS and OGLE data sets, on the other hand,
only allows the determination of an \emph{upper} limit in this range of masses,
making the overall result less robust. The optical depth analysis gives a very
good agreement between the observed and the expected values, and we show that
the available data do not allow one to discriminate between different bulge
models.
