This is a randomised, double-blind, placebo controlled trial over 52 weeks. Patients will be on one of four combinations of medications at the time of entry into the study: a) lithium and risperidone, b) lithium and olanzapine, c) valproate and risperidone, or d) valproate and olanzapine. After obtaining informed consent, patients will be randomised to one of three groups 1)"0" week group: patients will receive lithium or valproate plus placebo for 52 weeks (risperidone or olanzapine tapering will begin on the day of randomisation with discontinuation of the drug within 2 weeks), 2) continuation of the same atypical antipsychotic, risperidone or olanzapine, plus lithium or valproate for 24 weeks (tapering of the antipsychotic begins at the end of 24 weeks and completed within 2 weeks) followed by the same mood stabilizer plus placebo for another 28 weeks, and 3) continuation of the atypical antipsychotic, risperidone or olanzapine, plus lithium or valproate for 52 weeks. The duration of the double-blind phase of the study will be 52 weeks and all patients will continue on the mood stabilizer, lithium or valproate, they had been on during the acute mania for the full duration of the study. The serum level of the mood stabilizer will be maintained within the therapeutic range (0.6 to 1.2 mmol/L for lithium and 50 to 125 ug/L for valproate) throughout the 52 weeks as determined by blood tests. The dose and the type of atypical antipsychotic (ie risperidone or olanzapine) each patient will receive during the double-blind period will be the same that the patient had been on at the time of entry into the double-blind phase. All patients, irrespective of which treatment arm they are in, will receive active psychoeducation and counselling regarding sleep hygiene, healthy daily routines and rhythms, alcohol and substance abuse, anxiety management, conflict resolution and problem solving as clinically indicated in routine clinical practice. Patients who withdraw from or meet a primary end point of the study will be treated actively as done in regular clinical practice.