To compare the efficacy and safety of quetiapine fumarate given as mono-therapy or adjunct therapy to lithium in the treatment of patients with acute mania in bipolar disorder. Patients with a documented clinical diagnosis of bipolar mania according to DSM-IV criteria (296.4X Bipolar I Disorder, Most Recent Episode Manic; 296.0X Bipolar I Disorder, Single Manic Episode) are required to have a YMRS total score of ≥20 at enrolment and randomisation