The effect of an orally active immune modulator on growth and feed utilization in chronic antigen-challenged pigs was evaluated. In each of 16 litters, four pigs were allotted from each litter to one of four dietary concentrations (0, 22, 44, or 66 ppm) of peptidoglycan derived from Bifidobacterium thermophilum. The pigs were derived from a single herd, weaned at 10 to 16 days of age, placed in nonsanitized nursery, and orally exposed to excreta of older pigs in the base herd at 4-day intervals from 9 to 76 lb body weight. Pigs were individually penned and allowed to consume feed and water ad libitum. Daily gains and feed/gain ratios of pigs were not altered by dietary peptidoglycan concentrations. Based on these data, dietary additions of peptidoglycan did not enhance the growth performance of chronic antigen-exposed pigs.