In this paper, we propose a novel IC diagnosis approach, based on probabilistic differential quiescent current (I/sub DDQ/) signatures. Unlike the previous diagnosis approaches using current, this approach, using the maximum likelihood estimation, provides a solid framework allowing to quantify its robustness with respect to current measurement variations. The differential nature of the signatures allows to treat subthreshold leakage currents as a noise source. Results are provided showing the robustness of the approach. The applicability of the approach on embedded logic is also briefly discussed.