Asymmetric dimethylarginine, symmetric dimethylarginine, and L-monomethylarginine are originated from the subsequent proteolytic catalysis of methylated arginine residues on different proteins and inhibit the endogenous nitric oxide generation. The changes in total methylarginine load (Asymmetric dimethylarginine plus symmetric dimethylarginine plus L-monomethylarginine) may contribute to hypertension. The aim of this study was to determine serum methylarginine concentrations in patients with masked hypertension and determine the association between these biomarkers and blood pressure measurements. Control group, masked hypertension and hypertension groups consisted of 40 subjects (11 males, 28 females, mean age 48.6 ± 13.1), 28 subjects (14 males, 14 females, mean age 50.9 ± 11.0) and 36 subjects (15 males, 21 females, mean age 54.4 ± 12.3 years), respectively (P= 0.149). Serum total methylarginine load was significantly higher in hypertension group (0.63 ± 0.23) compared to masked hypertension (0.49 ± 0.16) and control groups (0.38 ± 0.13) (P= 0.008 and P< 0.001). While there was no statistically significant difference between healthy control groups [0.147 (0.03–0.29)] and masked hypertension patients [0.144 (0.05–0.42)] for serum symmetric dimethylarginine levels (P= 0.970), it was markedly elevated in hypertension group [0.25 (0.07–0.54)] compared to masked hypertension group [0.14 (0.05–0.42)] (P= 0.001). Serum total methylarginine load was positively correlated with night-time SBP (r = 0.214, P= 0.029). Serum methylarginine levels might be a useful marker for determining the courses of clinical hypertension.