Six ruminally-fistulated steers were used to evaluate the effect of Rumensin and feed intake variation on ruminal pH. Steers were adapted to a 92.5 percent concentrate diet and then subjected to three levels of intake variation: ad libitum, intake variation of 2 lb/day, and intake variation of 4 lb/day. Feed intakes and ruminal pH were monitored continuously throughout the entire trial. Results indicate that Rumensin reduced acidosis by elevating average ruminal pH and decreasing are of ruminal pH below 5.6. In addition, Rumensin stabilized rate of intake and daily ruminal pH fluctuation at the high level of intake variation