To better explore the clinical heterogeneity of bipolar mood states, we developed a dimensional scale for assessing all mood episodes (depressive, hypomanic, manic, mixed states) using the same tool. The Multidimensional Assessment of Thymic States (MATHYS) (Henry et al., 2008) provides two scores, a total score measuring a level of activation and a sub-score of emotional reactivity. The aim of this study was to establish the appropriate cut-off in total activation versus inhibition and in the emotional reactivity sub-score in bipolar disorders. Patients (n=187) during an acute episode and controls (n=89) filled in the MATHYS. Receiver Operating Characteristic (ROC) curves were obtained to estimate the sensitivity and specificity of the global score and the emotional reactivity sub-score of the MATHYS, in order to differentiate patients from controls. ROC curves showed very satisfactory sensitivity and specificity levels both for the total score and the sub-score of emotional reactivity, thus providing an appropriate cut-off. Concerning the total score between 0 and 200, patients with a score lower than 91 had significant global inhibition and those with a score higher than 109 had significant global activation. Regarding the emotional reactivity sub-score between 0 and 40, patients with a score lower than 16 had significant emotional hyporeactivity and those with a score higher than 24 had significant emotional hyperreactivity. Our results provide cut-offs for the MATHYS to identify patients in an acute phase.