The first analytical method for simultaneous speciation analysis of five of the most important gadolinium-based magnetic resonance imaging (MRI) contrast agents in blood plasma samples was developed. Gd-DTPA (Magnevist), Gd-BT-DO3A (Gadovist), Gd-DOTA (Dotarem), Gd-DTPA-BMA (Omniscan), and Gd-BOPTA (Multihance) were separated by hydrophilic interaction liquid chromatography (HILIC) and detected with electrospray mass spectrometry (ESI-MS). Spiking experiments of blank plasma with Magnevist and Gadovist were performed to determine the analytical figures of merit and the recovery rates. The limits of detection ranged from 1 x 10 (-7) to 1 x 10 (-6) mol/L depending on the ionization properties of the individual compounds, and limits of quantification ranged from 5 x 10 (-7) to 5 x 10 (-6) mol/L. The linear concentration range comprised 2 orders of magnitude. With application of this method, blood plasma samples of 10 healthy volunteers, with Magnevist or Gadovist medication, were analyzed for Gd-DTPA and Gd-BT-DO3A, respectively. The obtained results were successfully validated with inductively coupled plasma-optical emission spectroscopy (ICP-OES).