Four growth trials and one digestibility trial were conducted to determine the effects of substituting barley for grain sorghum in weanling pig diets on pig performance and nutrient digestibility. Experiments 1 and 2 were 35-d growth trials in which barley was substituted for gain sorghum at levels of 0, 10, 20, 30 and 40% of the diet. Average daily gain (ADG), average daily feed intake (ADFI) and feed conversion (F/G) were not affected by dietary barley level (P greater than .50). Experiment 3 was a digestibility trial conducted to determine the apparent digestibility of dry matter (DMD), gross energy (GED), and N (ND) and percentage of N retained (%NRT) of pigs fed the 0, 20 and 40% barley diets. As dietary barley level increased, DMD and GED decreased linearly (P less than .05), whereas %NRT increased linearly (P less than .10). Apparent N digestibility was not affected by dietary treatment (P greater than .12). Experiments 4 and 5 were 35-d growth trials with treatments arranged in a 2 x 3 factorial design to determine the effects of barley particle size (fine, 635 microns or medium, 768 microns) and dried whey level (0, 10 or 20%) on pig performance. Average daily gain and ADFI increased linearly (P less than .01) as whey level increased. Pigs fed diets containing fine-ground barley grew faster and were more efficient (P less than .05) than those fed medium-ground barley diets.(ABSTRACT TRUNCATED AT 250 WORDS)