Two experiments were carried out to evaluate the effect of dietary addition of yeast cell wall (YCW); beta-1, 3/1, 6-glucan (BG); and mannoprotein complex (MP) purified fractions in broilers. In experiment 1, there was a control diet and 5 experimental diets containing, respectively: 10 mg of avilamycin (AVI)/kg of feed, 500 mg of YCW/kg of feed, 95 mg of MP/kg of feed, 145 mg of BG/kg of feed, and 95 mg of MP plus 145 mg of BG/kg of feed. All birds were vaccinated via drinking water against Newcastle disease virus at 9 d of age. At 42 d, chickens fed AVI, YCW, MP + BG, and BG diets had similar BW not significantly different from chickens fed the control diet. The antibody response of Newcastle disease virus vaccine was not affected by any experimental treatment. Broilers fed MP + BG diet had greater thymus weights (P </= 0.05), as a percentage of BW than those from the control and AVI treatments, but similar with respect to YCW and BG treatments. In experiment 2, there was a group-fed basal diet and 3 additional experimental groups receiving the basal diet supplemented with, respectively: 500 mg of YCW/kg of feed, 190 mg of MP/kg of feed, and 227 mg of BG/kg of feed. At 42 d of age, no difference in broiler growth rates was observed. Samples of the jejunum were collected at 21 d of age to determine villus height. Significantly higher villus height was observed in YCW, MP, and BG groups compared with that of the control group. The relative percentage of liver weight (P </= 0.01) was lower in broilers fed YCW than in broilers fed the control diet, but no differences were observed in respect to chickens fed BG. Data of these studies suggested that the changes in thymus and liver relative weights and villus morphology of broilers were induced with the same intensity by the use of complete YCW, MP + BG, and BG supplements.