Six experiments were conducted at 3 geographic locations to determine the effect of 0 and 2 g of bambermycins5/ton of complete feed upon ADG in growing-finishing swine from 35 kg body wt to market. A 6.6% significant improvement in ADG and a 6.1% significant improvement in F/G over the control pigs was observed with the 2 g bambermycins treatment. The performance was divided into growing and finishing periods. In the growing period, bambermycins significantly improved ADG and F/G by 4.3 and 5.1%, respectively. The finishing period response was significant at 8.1 and 7.4% for ADG and F/G, respectively. The percentage improvement in ADG and F/G was greater in the finishing period than during the growing period in these studies.