N-nitrosodimethylamine (DMN) is concentrated from ambient air on Tenax-GC in a short glass tube (1, 2). It is desorbed by heating and purging with helium into a liquid nitrogen-cooled nickel capillary trap and then introduced onto a high resolution gas chromatographic column where it is separated from interferences. The concentration of DMN is measured from the mass spectrometric signal at m/e 74 (3).