The effect of pre- and postweaning exposure to soybean meal on postweaning growth performance and immune response by the early-weaned pig was analyzed. In Exp. 1, treatments were assigned in a 2 x 2 x 2 factorial arrangement. Pigs were derived from gilts fed either a soybean meal- or a corn gluten meal-based diet during gestation and lactation. Six to eight pigs per litter were either stomach-infused with or without (placebo) soybean meal during d 5 to 9 after farrowing. At weaning, 240 pigs (initially 5.1 kg, 21 +/- 1 d) were randomly allotted to either a corn-soybean meal or a corn-dried skim milk-dried whey diet based on gilt and infusion treatments. Average daily gain, ADFI, and gain:feed ratio were decreased (P < .05) on d 0 to 14 postweaning for pigs fed a soybean meal diet compared with pigs fed a milk diet. Skin-fold thickness after intradermal injection of soy protein and casein extracts on d 6 and measured on d 7 postweaning was not affected (P > .10) by dietary treatment, but serum immunoglobulin G titers to soybean glycinin and beta-conglycinin were increased (P < .01). From d 14 to 35 postweaning, all pigs were fed a common (1.25% lysine) corn-soybean meal diet containing 10% dried whey. Average daily gain, ADFI, and gain:feed ratio were decreased (P < .05) from d 14 to 35 for pigs fed a milk diet on d 0 to 14 postweaning. Serum immunoglobulin G titers were higher (P < .01) on d 21 postweaning for pigs fed soybean meal for the entire nursery period. Cumulative ADG (d 0 to 35) and gain:feed ratio were decreased (P < .05) for pigs fed a milk diet from d 0 to 14 compared with pigs fed a soybean meal diet. In Exp. 2, 104 pigs (initially 5.3 kg, 21 +/- 1 d of age) were used to determine the effect of 0, 7.5, 15.0, and 22.5% soybean meal in a high-nutrient-dense starter pig diet. Differences were not detected (P > .10) in ADG, ADFI, and gain:feed ratio during d 0 to 14, but ADFI decreased (linear, P < .05) and gain:feed ratio increased (linear, P < .05) during d 14 to 35 and for the entire 35-d trial as the level of soybean meal increased.(ABSTRACT TRUNCATED AT 400 WORDS)