  We consider the Olsson sum rule, i.e., the forward dispersion relation for
pion-pion scattering with exchange of isospin unity at threshold. We show that,
if using the S0, S2 and P wave expressions of Colangelo, Gasser and Leutwyler,
then either the sum rule is not satisfied or, if adjusting the residue of the
rho exchange Regge amplitude to have the sum rule satisfied (as recently
proposed by Caprini, Colangelo and Leutwyler) then the subsequent high energy
amplitude is in disagreement with experimental pi-pi cross sections.
