Nitrates have been successfully fed to dairy cows to decrease methane emissions in several experiments. In the nitrate assimilatory pathway, bacteria reduce nitrate to nitrite to ammonia. Because the second step can be rate-limiting, nitrite accumulation poses health risks such as methemoglobinemia, which would hinder adoption of nitrate feeding to compete with methanogens for H₂ while assimilating the N from nitrate into microbial protein. The yeast Saccharomyces cerevisiae has the potential to anaerobically respire nitrite through its cytochrome c oxidase; it also can stimulate populations of bacteria that express nitrate and nitrite reductases. For this project, 4 dual flow continuous culture fermenters were used in 5 periods with 7 d of adaptation and 3 d of sampling. Fermenters were fed 40 g DM (50:50 ratio of concentrate:alfalfa pellet). Treatments were arranged in a 2 × 2 factorial with NO₃ (1.5% of DM) or urea as an isonitrogenous control and without or with Yea-Sacc (Alltech Inc., Nicholasville, KY) fed at a recommended 0.010 g/d. Gas production was measured over 3 d by closed circuit respirometry; 1 fermenter’s gas production was omitted for all periods (unrelated to treatment). Objectives were to test the hypothesis that the combination of live yeast culture and nitrate would mitigate methane production in continuous culture compared with the control (a statistical interaction). However, there were no interactions (P > 0.10). The main effect of nitrate decreased (P < 0.05) CH₄ emission compared with urea control (29.6 vs 21.0 mmol/d). There was no difference (P > 0.10) for H₂ emission for nitrate or yeast (averaging 0.149 mmol/d; SEM = 0.051), but the main effect of nitrate was decreased (P < 0.01) for aqueous H₂ concentration compared with urea (1.23 vs 1.88 µM). Total VFA production (averaging 148 mmol/d; SEM = 15) and acetate:propionate (averaging 3.37, SEM = 0.12) did not differ (P > 0.10) among treatments. Nitrate decreased methanogenesis without affecting H₂ variables. No interactions were detected, but live yeast might offer a useful protection against incompletely adapted rumen microbial populations.