A nitrogen balance experiment was conducted to study the individual and group response of growing pigs to threonine (Thr) intake. A series of fifteen purified diets with increasing concentration of Thr was fed sequentially to nine pigs during a 15-d experimental period. The concentration of Thr ranged from 50 to 140% of its assumed requirement while other essential amino acids were given in a 25 % excess. N retention was related to Thr intake using rectilinear and curvilinear models. The quadratic-plateau model fitted the individual data significantly better (P=0.02) than the linear-plateau model. The R² statistic indicated that the group response of pigs to Thr intake was better described by the linear-plateau and quadratic-plateau models than by exponential, saturation kinetics or four-parameter logistic models. Significant differences (P=0.004) were found between individual plateau values in the linear-plateau model while the slopes of the regression lines did not differ. No significant correlation was found between the slope and plateau or breakpoint values of the linear-plateau model. Marginal efficiency of Thr utilization derived from the linear-plateau model was 0.67. In the quadratic-plateau model, marginal efficiency of Thr utilization was dependent on Thr intake and ranged from 0.77 (50% of requirement) to 0.42 (100% of requirement). Based on linear-plateau and quadratic-plateau models, daily requirement of Thr for a 45 kg pig was calculated to be 11.5 and 12.1 g, respectively