True digestible lysine requirements of PIC barrows were estimated by using a PUN (plasma urea nitrogen) technique. For the individually penned barrows, daily true digestible lysine requirements were 16.5, 17.8, 19.9, 20.2, 17.4, 16.7, 16.9, and 14.4 grams at the body weights of 33, 52, 69, 72, 87, 93, 106, and 113 kg, respectively. Based on the results, a lysine requirement model of the pigs over the growing and finishing period under an individually penned environment was established. The equation was y = 0.000001x⁴ - 0.0004x³ + 0.0365x² - 1.329x + 32.691, in which y is the true digestible lysine requirement in grams /day, and x is the body weight in kilograms. True digest lysine requirements of the pigs under a group-penned environment were determined to be 15.8 and 19.1 g/d, at 32 and 50 kg body weight, respectively.