A method is described for the quantitation of muramic acid, a marker of bacterial peptidoglycan, in organic dust. House dust samples were hydrolysed in hydrochloric acid and then extracted with hexane to remove hydrophobic compounds. The aqueous phase was evaporated, heated in a silylation reagent to form trimethylsilyl derivatives, and analysed by gas chromatography--mass spectrometry. The muramic acid derivative gave two peaks upon injection into the gas chromatograph--mass spectrometer. Injection of 10 pg of the derivative gave a signal-to-noise ratio of 17 for the dominating peak when using selected ion monitoring in the electron impact mode, and a linear calibration curve was achieved upon analysis of samples containing 5-1500 ng of muramic acid. In a house dust sample, 40 ng of muramic acid was found per mg of dust; the coefficient of variation was 8.2% (n = 6, 1.2 mg of dust analysed). The described method is rapid and simple to apply, and should therefore become widely used for measuring peptidoglycan in many types of environmental samples, including organic dust.