I report on preliminary measurements of the tt̄ production cross section, and a measurement of the top quark mass, performed by the DØ Collaboration. The cross section is measured using candidates for dilepton, single-lepton, and all-hadronic tt̄ decays collected at DØ during RunII of the Tevatron. The results for the various modes are: σ tt̄=14.3 -4.3 +5.1(stat.) -1.9 +2.6(syst.)±0.9(lumi.)pb(dilepton) σ tt̄=7.2 -2.4 +2.6(stat.) -1.7 +1.6(syst.)±0.5(lumi.)pb(lepton+jets) σ tt̄=7.7 -3.3 +3.4(stat.) -3.7 +4.7(syst.)±0.5(lumi.)pb6(all-hadronic). The mass measurement uses an improved method to re-analyze lepton+jets events collected during RunI of the Tevatron, and obtains m t = 180.1 ± 3.6 (stat.) ± 4.0 (syst.) GeV/c 2.