Two experiments were conducted to evaluate the effects of live yeast supplementation on performance, nutrient digestibility, enteric microbial populations and volatile fatty acid (VFA) concentration of weanling pigs, receiving diets supplemented with aureomycin and elevated doses of CuSO4. In experiment 1, 90 crossbred pigs (7.20 +/- 0.44 kg, 28 d of age) were randomly allotted to one of five dietary treatments containing either 0, 4.0 x 10(6), 9.0 x 10(6), 2.6 x 10(7), or 5.1 x 10(7) cfu Saccharomyces cerevisiae per gram with six replicate pens per treatment and three pigs per pen. BWG and feed intake increased quadratically during days 1-14 and days 1-28 as live yeast levels increased (p < 0.01). Pigs fed the diet containing 2.6 x 10(7) cfu yeast per gram had the highest BWG and feed intake among the treatments. In experiment 2, 48 crossbred pigs (7.64 +/- 0.72 kg, 28 d of age) were fed diets containing live yeast at 0 or 3.2 x 10(7) cfu of S. cerevisiae per g with six replicate pens per treatment and four pigs per pen. The yeast supplementation improved BWG and feed intake during days 1-14 (p < 0.01) and days 1-28 (p < 0.05). Treatment differences were not observed in any of the bacterial populations, yeast numbers or VFA concentrations, at any of the sites of the gastrointestinal tract tested. Total tract nutrient digestibility was also not different between treatments. Overall, dietary supplementation of live yeast had a positive effect on BWG and feed intake of weanling pigs, receiving diets supplemented with aureomycin and elevated doses of CuSO4. The improvement in BWG appears to be partly related to an increase in feed intake. The mechanism of yeast improving feed intake of piglets needs to be explored.