Four hundred and fiftynewly weaned nursery pigs were observed over a 35-day period at the Iowa State University Swine Nutrition Farm. Pigs were weighed and allotted to 1 of 5 treatments upon arriving, averaging 6.49 ± 0.40 kg for an initial bodyweight. All pigs were had ad libitumaccessto feed and water. The 5 treatments consisted of differing ratios of SID tryptophan to lysine, as follows: 0.150 Trp:Lys, 0.175 Trp:Lys, 0.200 Trp:Lys, 0.225 Trp:Lys, and 0.250 Trp:Lys. The overall data indicate that there is no further advantage in termsof growth performance and feed efficiency by having a diet containing a Trp:Lys ratio greater than 0.175 for nursery pigs. The Trp:Lys ratio largely explained variation in feed efficiency, but not ADG or ADFI. These data are supportive of the Trp:Lys ratio (Trp:Lys = 0.170) specified by the NRC (2012).