Nine ruminally cannulated steers (average weight 477 kg) were randomly assigned to serve as controls (C) or to be fasted (F) or fasted and transported (FT). C steers were allowed free access to alfalfa hay, water and plain salt during the experiment; F steers were deprived of feed and water for 32 hr, and FT steers were deprived of feed and water and transported for 32 hr in a gooseneck trailer. After 32 hr, F and FT steers were allowed access to alfalfa hay, salt and water. Rumen samples were withdrawn via cannula at 0, 18, 32, 36, 46, 56, 80 and 104 hr after the start of the experiment. Jugular blood was sampled at the same times, except for 36 and 46 hours. Rumen pH of F and FT steers increased (P less than .05) during the 32 hr fasting/transit period over that of C steers and then decreased (P less than .05) on refeeding. Total VFA concentrations were lower in F steers (39.5 mmoles/liter) at 32 hr than in FT steers (202.2 mmoles/liter). Total counts of rumen bacteria and protozoa were lower (P less than .05) in F and FT steers than in C steers at all times except 0 and 104 hr, and recovery of microbial numbers was slower in FT and in F steers. VFA data suggest rumen motility may be impaired in FT steers compared with that in F steers. Blood glucose was higher (P less than .05) at 18 an 32 hr in FT than in F steers. Serum glutamic oxaloacetic transaminase was higher (P less than .05) at 18 hr (104.7 IU/liter) in FT steers than in steers in the other two groups (average 84.3 IU/liter). Serum Fe tended to be lower at 18 and 32 hr in FT steers than in F and C steers, and serum triglycerides were lower (P less than .05) in FT steers at 32 and 56 hr than in C. Most other blood constituents were not greatly affected by treatment. These data suggest that the physiological response of fasting alone differs considerably from that of fasting and transit stress, because transit appears to impose influences on rumen fermentation and blood chemistry beyond those imposed by fasting.