Objective: This study was set up to investigate the relationship between immune process and high levels of human chorionic gonadotropin-beta (beta hCG) in hyperemesis patients with or without hyperthyroxinemia. Methods: beta hCG, immune parameters and thyroid related hormones were assayed in hyperemesis patients and in controls. Results: Mean serum beta hCG, fT4 and TSH levels were significantly higher in hyperemesis patients than in controls (p < 0.01, p < 0.01, p < 0.05, respectively). Further, immune parameters regarding IgG, IgM, C3 C4 and lymphocyte count were significantly higher in patients than in controls (p < 0.05, p < 0.01, p < 0.01, p < 0.05, p < 0.01, respectively). In hyperemesis patients with hyperthyroxinemia, mean serum beta hCG, IgG and IgM were significantly higher than in hyperemesis women without hyperthyroxinemia (p < 0.001, p < 0.05, p < 0.05, respectively). beta hCG was positively correlated with fT4 (r = 0.45, p < 0.05), with lymphocyte count (r = 0.47, p < 0.01), with IgM (r = 0.38, p < 0.05) and with C3 (r = 0.40, P < 0.05) in hyperemesis patients. A negative correlation between beta hCG and ISH (r = -0.43, p < 0.05) was noted in the hyperemesis group. Free T-4 showed a positive association to IgM (r = 0.49, p < 0.01), to IgG (r = 0.40, p < 0.05), to lymphocyte count (r = 0.45, p < 0.05). Conclusion: Immunologic activity in pregnancy may have an effect or role on the stimulatory mechanism of beta hCG in hyperemesis patients with or without hyperthyroxinemia.