  The results on the measurements of the top-quark mass, based on the data
collected by the Tevatron experiments CDF and D{\O}at Fermilab during Run I
from 1992 to 1996, and Run II since 2001 are summarized. The combination of the
published Run I and preliminary Run II results, taking correlated uncertainties
properly into account, is presented. The resulting preliminary world average
for the mass of the top quark is: $\MT=174.3 \pm 3.4 \GeVc2$, where the total
error consists of a statistical part of $2.0 \GeVc2$ and a systematic part of
$2.8 \GeVc2$.
