Impacts of feeding live yeast, probiotic bacteria, or a combination on the performance and apparent total-tract digestion in 3 mo old steers. Experimental design was an incomplete replicated 4 × 4 Latin square design with 4 replicates and 3 periods. Sixty-four calves were blocked by initial BW and randomly assigned within blocks to a pen with 3 calves per pen. Dietary treatments were arranged as a 2 × 2 factorial and included: Control, no supplement; Yeast, supplemented with 1.0 × 1010 cfu/d live Saccharomyces cerevesiae; Probiotic, supplemented 2.5 × 109 cfu/d of a blend of Enterococcus faecium and Lactobacillus casei; or Combination, supplemented with both the Yeast and Probiotic treatments. Periods consisted of a 10 d adaptation period followed by a 4 d collection period. Individual BW were measured at the beginning and end of each collection period and feed intake daily. Fresh fecal samples were collected from the surface of each pen 8 times during the collection period and composited for subsequent nutrient analyses and calculation of apparent total-tract nutrient digestibility using iNDF240. The model included the fixed effects of Yeast, Probiotic, and their interaction. Period was included as a random intercept and treatment nested within pen was the subject of the repeated statement. There was a tendency (P = 0.057) for calves fed Yeast to have increased DMI (4.44 vs 4.22 ± 0.44 kg/d). The ADG of all treatments tended (P = 0.054) to be greater when compared with the Control (1.41, 1.44, 1.39, and 1.26 ± 0.16 kg/d for Yeast, Probiotic, Combination, and Control, respectively). There were no differences (P ≥ 0.189) in apparent NDF or CP digestibility, but there was a tendency (P = 0.064) for a Yeast × Probiotic interaction on ADF digestibility (30.9, 32.0, 29.8, and 29.7 ± 0.90% for Yeast, Probiotic, Combination, and Control, respectively). Data indicate that supplementing growing steers with specific active dry yeast or probiotic bacteria can influence fiber digestibility and improve performance, but the mechanisms of action may be different.