Highly sensitive and specific analytical GC-MS procedures were developed and comprehensively validated for the determination of the opioid narcotics fentanyl, sufentanil and alfentanil and their major nor-metabolites in urine of potentially exposed opioid production workers. A simple, one step extraction protocol was developed using commercially available solid phase extraction (SPE) columns to recover all analytes from urine. The secondary amine functionalities of the nor-metabolites were derivatized to form stable, pentafluorobenzamide (PFBA)-derivatives with good chromatographic properties. Using the penta-deuterated analogues as internal standards, a limit-of-detection (LOD) of 2.5 pg fentanyl/ml, 2.5 pg sufentanil/ml and 7.5 pg alfentanil/ml urine was achieved. For the opioid metabolites the LODs were found to be <50 pg/ml urine. The developed analytical procedures show excellent intra-assay accuracy, particularly considering the ultra low levels of the analytes, with relative errors generally below 10%. Overall, an excellent reproducibility was observed with coefficients of variation below 10% at all spike levels for all opioid parent compounds and their metabolites, except for low norfentanyl concentrations. Upon storage at -30 degrees C urine samples were found to be stable for at least 2 months as no significant losses of either compound were observed. The developed analytical procedures have been successfully applied in a biological monitoring survey of fentanyl exposed production workers.