Opiates have a long history of treating mood disorders. Some researchers have suggested that changes in this system may trigger the switch to/from manic and depressive states in bipolar disorder. The clinical use of opiate medications has been limited by their abuse/dependence potential. Studies of opiate receptor subtypes have raised the possibility that medications targeting the kappa/dynorphin system could be used to target mood symptoms with reduced/limited addiction potential. Rodent studies at Mclean indicate that kappa-agonists have pro-depressant effects and kappa-antagonists have anti-depressant effects. In addition, antimanic/antipsychotic medications regulate the activity of dynorphin cells. This study is a pilot open-label investigation using Talwin, a combination of pentazocine and naloxone. Pentazocine is a kappa agonist and mixed mu agonist. Two doses of Talwin will be given to acutely manic inpatients in a cumulative-dosing strategy. Measurements of manic symptoms will be conducted before, during, and after administration. This study will determine whether pentazocine has an immediate or sustained impact on acute mania symptoms.