We report on a search for narrow-width particles decaying
to a top and antitop quark pair. The data set used in the analysis
corresponds to an integrated luminosity of 680 pb-1 collected with the
Collider Detector at Fermilab in Run II. We present 95% confidence level
upper limits on the cross section times branching ratio. Assuming a
specific topcolor-assisted technicolor production model, the leptophobic
Z' with width Gamma_Z' = 0.012 M_Z', we exclude the mass range M_Z' <
725 GeV/c2 at the 95% confidence level.