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A total of 36 individually penned barrows (initial weight = 176 lb) were used in an experiment conducted to determine the lysine requirement for barrows fed ractopamine during the last 85 lb of the fi nishing phase. There were six dietary treatments that were corn-soybean meal-based with additional crystalline amino acid supplementation. Pigs were assigned to one of six dietary treatments for the duration of the experiment. Treatments included lysine concentrations ranging from 0.5 to 1.3% total lysine. Dietary treatment significantly affected average daily gain and feed efficiency. The total lysine requirement was estimated to be 0.76%. These results indicate that the outcome of ractopamine utilization can be influenced by amino acid concentration of the diet in the finishing phase.