Mania is accompanied with immune activation as indicated by increased pro-inflammatory cytokines, acute phase proteins; and carcinoembryonic antigen (CEA) is known to accompany signs of immune-inflammatory responses in bipolar disorder (BD) and medical disorders. In this study, it was aimed to compare high sensitivity C-reactive protein (hsCRP), CEA levels and white blood cells (WBCs) counts in the treatment-resistant BD (Group 3), the treatment-responsive BD patients (Group 2), and the healthy control group (Group 1). The sociodemographic data form, the Young Mania Rating Scale (YMRS), the Hamilton Depression Rating Scale (HDRS), and the Clinical Global Impression Severity of Illness (CGI-S) Scale were applied to the patients. In Group 3, the WBCs counts, and CEA levels were significantly higher than the other two groups. There was a positive correlation between WBCs counts and YMRS and CGI-S scores in all manic patients. There was a positive correlation between CEA levels and YMRS, HDRS and CGI-S in manic patients. This study shows that there is an activation of the immune-inflammatory response system in treatment resistant manic patients; and, WBCs counts and CEA levels are associated with severity of disease in manic patients.