Organophosphorus flame retardants (OPFR), phosphorus triesters, are widely used chemicals with a high share of the worldwide flame retardant market. In animal experiments, dialkyl- and diarylphosphates are the main metabolites of OPFR. Therefore we elaborated a GC-MS/MS-method for the detection of OPFR-metabolites in human urine after solid phase extraction and derivatization with pentafluorobenzylbromide. The limits of detection range from 0.1 to 1 microg/l. Interday imprecision were 2-8%. The applicability of the method is shown by determination of the internal burden of 30 persons of the German general population. OPFR-metabolite concentrations range from <LOD to 27.5 microg/l for bis-(2-chlorethyl)-phosphate and <LOD to 4.1 microg/l for diphenylphosphate. Di-m-cresylphosphate and di-p-cresylphosphate cannot be detected in any of the native urine samples.