A method for design centering and tolerancing of tuned circuits, subject to environmental disturbances, is described. The region of acceptability is explored statistically, using a new method of gradient-based minimax optimisation with randomly chosen initial points. Nominal values and tolerances of continuous or discrete valued elements are determined from historgrams, which are built up from the analytical data collected during the exploration process. The method is illustrated by the design of two lossy, tunedLCladder filters.