We conducted two trials to determine the effects of replacing the lactose provided by spray-dried, edible-grade whey with edible-grade deproteinized whey or crystalline lactose on pig performance. In Exp. 1, 180 weanling pigs (initially 4.1 kg and 22 +/- 4 d of age) were allotted randomly to dietary treatments containing 18% lactose supplied by 1) 25% dried whey, 2) 12.5% dried whey and 9% crystalline lactose, 3) 18% crystalline lactose, 4) 12.5% dried whey and 10.9% deproteinized whey, or 5) 21.7% deproteinized whey. Casein was used to replace the lysine provided by dried whey in diets containing lactose and deproteinized whey. From d 0 to 14 after weaning, no differences (P > .10) were observed in ADG or ADFI. Pigs fed diets containing 18% crystalline lactose or 21% deproteinized whey had a higher (P < .05) gain:feed ratio (G/F) than did pigs fed diets containing 25% dried whey or 12.5% dried whey and 9% lactose. In addition, pigs fed diets containing 21% deproteinized whey had increased G/F compared to pigs fed the diet containing 10.9% deproteinized whey and 12.5% dried whey. In Exp. 2, 344 pigs (initially 4.4 kg and 14 +/- 2 d of age) were fed dietary treatments based on four sources of crystalline lactose replacing the lactose provided by dried whey in the positive control diet (20% dried whey). In addition, a negative control diet was formulated with 7.2% crystalline lactose. Casein was used to replace the lysine provided by dried whey. From d 0 to 14 after weaning, no differences (P > . 10) were observed in performance. However, pigs initially fed the positive control diet subsequently (d 14 to 28) consumed more feed than pigs fed the negative control diet. These results indicate that edible-grade deproteinized whey and crystalline lactose can replace the lactose provided by high-quality dried whey without affecting pig performance.