Two methods for the determination of methyl mercury (MeHg) in whole blood samples based on different mass spectrometric detection techniques are compared. The methods were employed in two studies in which the internal exposure of a group of mercury-exposed workers to total mercury and MeHg was investigated. Blood samples of these workers were analysed for MeHg independently from each other in two laboratories using similar extraction procedures but different detection techniques, viz. coupled GC-EI-MS/ICP-MS and GC-MS using D(3)-MeHg as internal standard. MeHg was detected in all blood samples in concentrations ranging from 0.3 to 9.0 microg/L. Though different detection techniques were employed, the results obtained by the two laboratories were in relatively good agreement.