Two experiments were conducted using newborn colostrum-deprived calves to establish the distribution of uptake of ¹²⁵I- globulin in smail intestine and to investigate effects of added microorganisms on ¹²⁵I-gamma globulin uptake. Ten calves less than 12.5 h of age (X̅ = 7 h) were anesthetized and intestines exteriorized through an abdominal incision. Intestine was ligated into 10 cm segments at 70 cm intervals beginning at the ileocecal junction, injected with ¹²⁵I-gamma globulin in an electrolyte solution and incubated for 1.5 h. One additional segment was formed adjacent to segments 1, 5 and 10 to assess effects of .5 h exposure to ¹²⁵I-gamma globulin on uptake by epithelium. After prescribed gamma globulin exposure, segments were excised, volume of lumen contents, segment weight and tissue activity were determined. Age, birth weight and intestine length were recorded. Location of each segment (PSEG) was expressed as percentage of distance from cecum to abomasum. Uptake was expressed as milligrams gamma globulin internalized per gram of segment tissue. Distribution of gamma globulin uptake after 1.5 h exposure was a cubic function of PSEG. Uptake was greatest In a region 15% of cecumabomasum distance, declining progressively towards the abomasum. After .5 4 exposure, regression of uptake on PSEG was a quadratic function with greatest uptake at 30% of cecum-abomasum distance. Uptake after 1.5 h exposure was greater than after .5 h. In experiment II, 10 calves less than 14 h of age (X̅ = 8.6 h) were anesthetized and intestines surgically exteriorized. Intestine was ligated into segments 10 cm in length at three cm intervals beginning 1.8 m above the ileocecal junction. Seven treatments were assigned in random order to segments in three successive sections of small intestine. Three treatments compared uptake in segments receiving one ml of either live intestine origin bacteria culture, sterile microbiological broth or autoclaved bacteria culture with four h incubation followed by 1.5 h exposure to ¹²⁵I-gamma globulin. Two treatments measured anaerobic microbial growth after four h incubation with one ml of either sterile broth or live bacteria culture. Residual ¹²⁵I-gamma giobulin was measured in segments receiving one ml of sterile broth or live bacteria culture with 5.5 h incubation followed by 15 second exposure to ¹²⁵I-gamma globulin. Measurements were as described for the first 10 calves. Serum corticosteroids, total protein and protein components were measured at O h and 5.5 h later. Uptake was lowest in segments receiving live bacteria as compared to segments receiving sterile inocula. Number of bacteria per gram of segment tissue was negatively correlated with uptake. Low serum corticosteroids were associated with low gamma globulin uptake. Body weight and age were not related to uptake in either experiment.in a decisive manner. / Ph. D.