In this study, whole-cell recordings of mitral/tufted cells (M/TCs) in the olfactory bulb of awake mice revealed greater hetereogeneity of activity compared with that in mice in an anaesthetized state, including in a subpopulation of cells with high spontaneous baseline activity and a subpopulation with very low levels of spontaneous activity. Interestingly, the silent and active subpopulations responded to odour exposure with depolarization and strongly increased firing rates or weak responses, respectively. These findings suggest a previously unrecognized level of complexity for odour processing.