A method is presented for the determination of the nitroimidazole drug dimetridazole (DMZ) in poultry tissues and eggs by liquid chromatography (LC)–thermospray mass spectrometry (MS). Deuteriated DMZ was employed as an internal standard. Samples were extracted with dichloromethane (muscle) or toluene (liver, egg) and applied to silica gel cartridges. Dimetridazole was eluted with acetone and the eluate evaporated to dryness at 40 °C under nitrogen. The residue was redissolved in methanol–water (1 + 1, v/v) and washed with hexane before LC–MS analysis. Quantification was by the ratios of the positive [M + H] ⁺ ions at m/z 142 and 145 for DMZ and the internal standard, respectively. Internal standard corrected recoveries were between 93 and 102% with RSDs between 1.2 and 7.7% for liver spiked at 5, 10 and 20 ng g ^{- 1} and muscle and eggs spiked at 5 ng g ^{- 1} . Absolute recoveries were approximately 80%. The method is suitable for statutory residue testing and was used to measure DMZ residues in eggs from chickens fed a diet containing DMZ at 10 mg kg ^{- 1} .