We present a new analysis of the dynamics of the planetary system around th
e pulsar B1257 + 12. A semianalytical theory of perturbation between terres
trial-mass planets B and C is developed and applied to improve the multiorb
it timing formula for this object. We use numerical simulations of the puls
e arrival times for PSR B1257 + 12 to demonstrate that our new timing model
can serve as a tool to determine the masses of the two planets.