Arterial hypertension is associated with increased plasma levels of complement C3, C4, and C-reactive protein (CRP). The aim of the study was to compare these laboratory markers in patients with resistant arterial hypertension (RAH) and controlled arterial hypertension (CAH). Patients with RAH (n=34), those with CAH (n=34), and 26 normotensive controls were included. White blood cell count, erythrocyte sedimentation rates, and blood levels of complement components C3, C4, and high-sensitivity C-reactive protein (hs-CRP) were compared among the study groups. In the RAH group, serum C3 (183.9±47.5 mg/dL) and hs-CRP (6.9±5.8 mg/L) were higher than in the CAH group (C3, 123.1±42.3 mg/dL; P<.001, hs-CRP, 4.2±4.8; P=.021, respectively). Significant positive correlations between systolic blood pressure and C3 (r=0.6481; P<.001) and hs-CRP (r=0.3968; P=.02) were observed in the RAH group. RAH is associated with higher blood levels of C3 and CRP.