A rapid and sensitive headspace gas chromatographic and mass spectrometric (GC-MS) method was developed for the determination of acrolein in human urine. A 0.5-ml urine sample in a glass vial containing propionaldehyde as an internal standard was heated at 80 degrees C for 5 min. A 0.1-ml volume of headspace vapor was injected into a GC-MS instrument. Acrolein and propionaldehyde were coeluted at 3.1 min using a DB-1 capillary column, and well separated by selective ion monitoring (SIM) mode using ions m/z 56.05 and m/z 58.05. The interassay and intraassay coefficient of variation were 0.99% and 3.3%. The calibration curve demonstrated a good linearity throughout concentrations ranging from 1 to 1000 nM. However, due to a wide variation of acrolein evaporation rates from human urine, a calibration curve must be established for each urine specimen using a standard addition method and detection limit varied from 1 to 5 nM. The total analysis time for two samples from one urine specimen required about 15 min. Therefore, this method is convenient for the urgent monitoring of urinary acrolein in patients to whom alkylating agents are administered.