MEKC with DAD was applied to detect six Gd-based contrasting agents (CAs) (Gd-DTPABMA (Omniscan), Gd-HPDO3A (ProHance), Gd-DOTA (Dotarem), Gd-AAZTA, Gd-BOPTA (Multihance) and Gd-DTPA (Magnevist)) commonly used in MRI diagnostics. The achieved LODs ranged between 0.40 and 20 mu M and the optimized method gave excellent precision, especially when two internal standards were applied (less than 0.34 RSD% for migration time). The MEKC technique made it possible to determine the CAs in urine and serum samples of patients having a therapeutic dose. Due to the SDS content of the running buffer, the serum samples can be directly injected to analyze Gd-based CAs without interference of high protein content.