The authors evaluate the impact of a synergistic preparation (SP) of supplements (a combination of calcium phosphomycin and tylosine tartarate) on the performance of broilers with a history of carcass condemnation at slaughter. The experiment included 120-day old broilers (Ross 308), divided equally into two treatment groups, with three replicates per treatment and 20 birds per replicate. The two groups included controls that did not receive SP and those that were treated with SP. The SP group received treatment at three intervals (at 1-5 days of age: 160 mg/kg body weight; at 21-25 days of age: 80 mg/kg; and at 29-33 days of age: 80 mg/kg body weight). The administration of SP at a low level improved performance in SP birds compared to controls and also resulted in the lowest cumulative mortality (1.67% vs 6.67%, respectively), the lowest feed conversion of 1.91 between 1 and 43 days of age and the highest live body weight (2,544.75 g vs 2,390.18 g). The administration of SP at a low level improved performance and reduced the frequency of specific gross lesions at market age (tracheitis, lung congestion, breast blisters and bursal congestion).