We conducted two experiments to evaluate the interactions among lactose and protein sources in diets for segregated early-weaned pigs. In Exp. 1, 360 barrows (initially 5.3 kg and 19 +/- 2 d of age) were fed diets containing crystalline lactose (0, 20, and 40%), spray-dried animal plasma (0 and 7.5%), and soybean meal (0 and 20%) in a 3 x 2 x 2 factorial arrangement. We used a blend of select menhaden fish meal and casein to replace the lysine provided by soybean meal or animal plasma. Diets contained 1.7% total lysine and were fed from d 0 to 14 after weaning. Pigs were fed a common diet from d 14 to 34. From d 0 to 14 after weaning, ADG and ADFI increased with increasing dietary lactose when the diet contained soybean meal but decreased when soybean meal was not in the diet (lactose x soybean meal, P < .05 and .10, respectively). Pigs fed animal plasma had increased (P < .05) ADG and ADFI from d 0 to 14 but decreased (P < .05) ADG from d 14 to 34. In Exp. 2, 324 barrows (initially 3.7 kg and 10 +/- 2 d of age) were fed diets from d 0 to 10 similar to those used in Exp. 1 with the exception that extruded soy protein concentrate replaced the lysine provided by soybean meal or animal plasma. From d 0 to 10 after weaning, increasing lactose improved (linear, P < .05) ADG and ADFI, and pigs fed animal plasma had higher ADFI (P < .05). In conclusion, soybean meal had no negative effect on ADG; however, animal plasma and lactose increased ADG and ADFI for pigs weaned between 10 and 19 d of age.