The objective of this study was to determine the Ile requirement for maintenance using the indicator AA oxidation method. Each of six sows, non-pregnant after their 4th litter, received 6 diets based on corn, corn starch and sugar at a mean ADFI of 2.19 kg/d (SE 0.014). Diets were calculated to provide Ile at 10, 20, 30, 50, 60, and 70 mg/kg0.75 BW. Sows were confined in respiration chambers overnight before each oxidation study to determine fasting energy expenditure. The 13C background in expired CO2 was determined for 1.5 h. Sows were fed 2 mg/(kg BW·h) of L[1-13C]Phe over 4 h in 8 ½-hourly meals. Expired CO2 was analyzed for 13C enrichment above background. Requirements were determined as the breakpoint in indicator AA oxidation in 2-phase nonlinear models. Mean sow BW was 219 kg (SE 2.41). The ADG of -0.199 kg/d (SE 0.098) during the 18-d study was not different from zero (P = 0.10). The Ile requirement was 35 mg/d×kg0.75 (P= 0.001). Overall Phe retention was less than zero (-0.92 g/d, SE 0.125, P = 0.001) but not different from zero (P = 0.14) for Ile intake above the requirement at -0.53 g/d (SE 0.334). Fasting heat production was 19.3 MJ/d (SE 0.41) or 334 kJ/kg0.75 BW (SE 8.5). The mean of fasting and fed heat production was 31.8 MJ/d (SE 0.19) and energy retention was -0.14 MJ/d (SE 0.054), which was not different (P = 0.80) from zero. The fasting and fed respiratory quotient was 1.0 (SE 0.02) and 1.02 (SE 0.02), respectively. Because energy and protein retention were not different from zero, the determined value of 35 mg/d×kg0.75 therefore represents the Ile maintenance requirement. AA maintenance requirements are greater for modern pigs but their ratios remain similar.