We report on the measurement of the ttbar production cross section
obtained by CDF and D0 experiments with ppbar collisions at sqrt s = 1.8 TeV.
The analyses presented here refer to integral Ldt \approx 110 pb^-1 collected
at the Fermilab Tevatron collider during the run 1992-96.  About 85% of the
possible ttbar decays have been studied in different channels classified
according to the number of high-p_T leptons found in the final state.  The
production cross section has been measured in each individual channel and them
combined into a single value for each experiment, which is sigma_ttbar =
7.5^+1.9_ -1.6 pb for CDF and sigma_ttbar = 5.77 +/- 1.76 pb for D0.