Method validation was carried out by establishing linearity, intra and inter-assay accuracy and precision, limit of detection (LOD), limit of quantitation (LOQ) and recovery. In oral fluid, five sets of calibrators with THC at concentrations between 1 and 100 ng/mL and THC-COOH at concentrations between 1 and 200 ng/mL were prepared using 1 mL of diluted blank oral fluid (1:3 diluted with 0.1 M phosphate buffer) for each. The LOD and LOQ were estimated from extracted samples spiked with decreasing concentrations of the compounds, where the response of qualifying ions in SIM mode was equivalent to that as three and ten times as the background noise, respectively. Inter- and intra-assay accuracy and precision were determined by replicate analysis (n=4) at three different concentrations (4, 40 and 80 ng/mL for THC and 8, 80 and 160 ng/mL for THC-COOH). The extraction procedure was repeated independently on four successive days. The recovery of THC and THC-COOH was also determined by comparing the analysis of extracted and non-extracted spiked samples at the three different concentrations. In order to determine the recoveries, internal standards were added in the last step of the extraction procedure.