The influence of the low-frequency timing noise on the precision of
measurements of the Keplerian and post-Keplerian orbital parameters in binary
pulsars is studied. Fundamental limits on the accuracy of tests of alternative
theories of gravity in the strong-field regime are established. The
gravitational low-frequency timing noise formed by an ensemble of binary stars
is briefly discussed.Comment: 4 pages, contributed paper to the proceedings of the IAU167
colloquium on pulsars, Bonn, August-September 199