Microdialysis membranes (3 mm length x 200 μm i.d.) have been used to extract volatile analytes from aqueous samples into the gas phase and interfaced with fast gas chromatography. Gas-phase extracts generated from aqueous samples reach steady-state concentrations and are transported to the detector in 5 s. The recovery of the system ranges from 1.28% for toluene to less than 0.1% for ethanol. The lowest detectable concentration without preconcentration was 5 mM for most compounds using a flame ionization detector, and as low as 0.01 mM for more volatile hydrophobic analytes. When interfaced with a fast GC system, changes in aqueous phase concentrations were monitored with a temporal resolution of 10 s.