  The transversity distribution was recently extracted from deep-inelastic
scattering processes producing hadron pairs in the final state. Together with a
specific chiral-odd di-hadron fragmentation function, it is involved in the
elementary mechanism that generates a transverse-spin asymmetry in the
azimuthal distribution of the detected hadron pairs. The same elementary
mechanism was predicted to generate an analogous asymmetry when the hadron
pairs are produced in proton-proton collisions with one transversely polarized
proton. Recently, the STAR Collaboration has observed this asymmetry. We
analyze the impact of these data on our knowledge of transversity.
