  We summarize the top-quark mass measurements from the CDF and DO experiments
at Fermilab. We combine published Run-I (1992-1996) measurements with the most
recent preliminary Run-II (2001-present) measurements using up to 1 fb-1 of
data. Taking correlated uncertainties properly into account the resulting
preliminary world average mass of the top quark is Mtop = 171.4 +/- 1.2 (stat)
+/- 1.8 (syst) GeV/c2, which corresponds to a total uncertainty of 2.1 GeV/c2.
The top-quark mass is now known with a precision of 1.2%.
