The objectives of this research were 1) to evaluate CuS0₄ and a CU lysine complex (CuLys) as growth promotants for weanling pigs, 2) to assess the effects of feeding growth stimulating levels of Cu from both sources on dry matter digestibility (DMO) and mineral balance of finishing pigs, and 3) to examine the effect of feeding elevated CU on serum growth hormone and IGF-1 levels. Two trials (176 pigs) were conducted in which pigs were fed 0, 100, 150, or 200 mg/kg Cu from CUS0₄ or CuLys. Elevated Cu increased daily gain and feed intake linearly, with no difference between the sources. Dietary CU linearly increased liver, kidney (P < .001), and brain (P < .05) Cu stores. In the liver, the linear response between the sources was different (P < .001); pigs fed 200 mg/kg Cu from CuLys had the highest CU concentration. Serum CU increased linearly with no difference between the two sources. Serum mitogenic activity increased linearly during wk 1 to 2 and 1 to 5 (P < .05), with no difference between the two sources. Twenty-four barrows were used to examine the effect of Cu additions from both Cu sources on digestibility and mineral balance. Pigs fed Cu from CuLys tended to have greater DMD when compared with controls (P < .10), but percentage of Cu absorbed was not different among the treatments. Pigs fed Cu from both sources absorbed more eu than controls (P < .01), with no difference between sources. Pigs fed CuS0₄ (P < .027) and CuLys (P < .101) absorbed more Fe than controls but Zn balance was not affected. Twelve pigs were cannulated after 7 wk of growth to quantify the effect of elevated dietary Cu on circulating growth hormone and IGF-1 levels. Growth performance was not improved by added Cu, but efficiency of gain was greater for pigs fed Cu when compared with controls (P < .101). Baseline growth hormone secretion was greater in pigs fed Cu (P < .06) for three of four days; however, average concentrations were not affected by diet. Concentrations of IGF-1 were higher in control pigs (P < .05). / Ph. D.