In this preliminary report, we describe four patients in whom long-term lithium therapy was discontinued, combined with actigraphic monitoring to assess changes in motor activity and the sleep-wake cycle. Two patients experienced rapid relapse of manic symptomatology, while two remained stable throughout a 1-year follow-up. Actigraphic monitoring revealed disintegration of the sleep-wake cycle and increased motor activity in the relapsed patients only. It is suggested that actigraphic recordings can be used to monitor lithium discontinuation.