Antipsychotic agents have, for a long time, been used to alleviate the severe behavioral problems associated with manic episodes. Risperidone, widely used in the treatment of schizophrenia, has been shown to be effective in the treatment of manic and mixed episodes associated with bipolar disorders. This is a randomized, double-blind, placebo-controlled study to evaluate the effectiveness and safety of risperidone compared with placebo in the treatment of patients with bipolar disorder who are experiencing a manic episode. Patients receive study medication (risperidone or placebo tablets) to be taken orally once a day at gradually increasing doses during the first week to achieve optimal effectiveness, while minimizing any intolerance to the drug. By Day 4, the dose of risperidone is in the range of 1 to 6 mg/day, and treatment with risperidone or placebo tablets continues for 3 weeks. The primary measure of effectiveness is the change in the Young Mania Rating Scale (YMRS) total score from baseline to the end of treatment. Additional assessments of effectiveness include the Clinical Global Impression-Severity of Illness (CGI-S) scale; the Global Assessment Scale (GAS), which assesses the patient's level of functioning; and the Positive and Negative Syndrome Scale (PANSS), a scale for measuring psychotic symptoms. Safety assessments include the incidence of adverse events throughout the study; measurement of vital signs (temperature, pulse, blood pressure) and evaluation of the presence and severity of extrapyramidal symptoms by the Extrapyramidal Symptom Rating Scale (ESRS) at specified intervals; and clinical laboratory tests (hematology, biochemistry, urinalysis) at the start and end of the study. The study hypothesis is that daily treatment with risperidone is more effective than placebo, as measured by Young Mania Rating Scale scores, in the treatment of the manic phase of Bipolar I Disorder. Risperidone tablets,1 mg (or placebo tablets) taken orally once daily in the evening; dose of 3 mg on Day 1; dose range of 2 - 4 mg on Day 2; dose range 1 - 5 mg on Day 3; dose range 1 - 6 mg on Days 4 - 21. Doses may be increased or decreased at investigator's discretion.