  We report on the measurement of two-pion correlation functions from pp
collisions at $\sqrt{s}=900$ GeV performed by the ALICE experiment at the Large
Hadron Collider. Our analysis shows an increase of the HBT radius with
increasing event multiplicity, in line with other measurements done in
particle- and nuclear collisions. Conversely, the strong decrease of the radius
with increasing transverse momentum, as observed at RHIC and at Tevatron, is
not manifest in our data.
