Recently, certain studies have indicated that 2-oxo-3-hydroxy-LSD is present in urine at much higher concentrations than LSD. We determined LSD and 2-oxo-3-hydroxy-LSD in urine by GC-MS (Hewlett Packard 5970) after solid phase extraction on SPEC.PLUS MP1 disks (3 mL, 30 mg, Ansys, Irvine, CA, USA), using the method recommended for amphetamines and derivatisation with BSTFA. For 2-oxo-3-hydroxy-LSD-bis-TMS, the ions with m/z of 309 and 499 were used as quantification and confirmation ion respectively. In four samples containing between 561 and 7007 pg/mL of LSD, 2-oxo-3-hydroxy-LSD concentrations between 8021 and 28466 pg/mL were found, i.e. 4 to 41 times higher than the LSD concentrations. 2-oxo-3-hydroxy-LSD does not seem to be conjugated. These results indicate that 2-oxo-3-hydroxy-LSD, is present in urine in much higher concentrations than LSD, which could facilitate confirmation of positive screenings and increase detection times.