The performances of two nominally identical automated monitors for quantifying volatile organic compounds were compared on identical ambient laboratory air samples. The monitors incorporate cryogenic preconcentration subunits specially designed for controlled release of liquid nitrogen to establish a -150 C trap temperature. Measured trends in concentration for perchloroethylene, toluene, and chloroform showed good agreement even at sub-ppbv levels during automated overnight runs, although some effects of adsorption were evident. In a second set of runs, concentration results for one system were plotted versus those for the other. The plots were linear and precise, but slightly biased, probably indicating a change in the system sensitivity between calibration and monitoring. Qualitative comparison using diluted automobile exhaust is also shown.