['Hemodialysis (HD) is associated with significant reductions in the plasma concentrations of the nitric oxide (NO) inhibitors N(G)-monomethyl L-arginine (L-NMMA), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). We sought to determine whether elevated concentrations of these NO inhibitors pre-HD and/or their acute decrease during HD might mediate intradialytic hypotension (IDH).', 'Systolic blood pressure (SBP), L-arginine, L-NMMA, ADMA, and SDMA were measured at the beginning (pre-HD) and at the end (end-HD) in 52 consecutive HD patients (age 64.4 +/- 13.4 years). IDH was defined as a SBP reduction of >20 mm Hg end-HD vs. pre-HD.', 'Fourteen patients demonstrated IDH. The mean SBP reduction during HD in this group was -35 +/- 13 mm Hg compared to an increase of +2 +/- 12 mm Hg among the 38 patients without IDH (no-IDH). Baseline demographic, clinical, and biochemical parameters did not differ between the IDH and no-IDH groups. However, the IDH group had higher pre-HD SBP (155 +/- 17 vs. 132 +/- 14 mm Hg, P < 0.001), pre-HD plasma SDMA concentrations (1.98 +/- 0.61 vs. 1.64 +/- 0.46 micromol/l, P = 0.04), and greater SDMA reductions during HD (-0.78 +/- 0.43 vs. -0.56 +/- 0.32 micromol/l, P = 0.06) than the no-IHD group. After adjusting for pre-HD SBP, the odds of IDH occurring were higher with increased pre-HD SDMA plasma concentrations (OR = 1.31 per 0.1 micromol/l SDMA increase; 95% CI = 1.04-1.65, P = 0.02) and with decreases in SDMA during HD (OR = 1.39 per 0.1 micromol/l SDMA decrease; 95% CI = 1.02-1.91, P = 0.04).'] Is symmetric dimethylarginine an independent predictor of intradialytic hypotension?