A method was developed for determining the occupational exposure to endosulfan and its main metabolites (endosulfanether, -lactone and -sulfate) in human urine using dieldrin as an internal standard. Solid phase extraction (SPE) and gas chromatography-tandem mass spectrometry (GC-MS-MS) have been used due to their high sensitivity and selectivity in avoiding most matrix interferences. The recovery efficiencies of the tested compounds yielded more than 89.2% at the fortification level of 10 ng ml(-1) in urine and their relative standard deviations were between 9.1 and 12.8%. The detection limit of each compound ranged between 6 and 18 pg ml(-1). Urine samples from nine pest control operators were analysed and total endosulfan concentrations between 94 and 2038 pg ml(-1) were found.