A robust control design on frequency domain using Mathematica is presented for regularization of glucose level in Type I diabetes persons under intensive care. The method originally proposed under Mathematica by Helton and Merino, [1] - now with an improved disturbance rejection constraint inequality - is employed, using the three-state minimal patient model of [2]. The robustness of the resulted high-order linear controller is demonstrated by nonlinear closed loop simulation in state-space, in case of standard meal disturbances and is compared with H∞ design implemented with the mu-toolbox of Matlab. The controller designed with model parameters represented the most favorable plant dynamics from the point of view of control purposes, can operate properly even in case of parameter values of the worst-case scenario. ©2006 IEEE.