||A Photovac 10S50 portable photoionization gas chromatograph mounted in a small automobile was used to sample air for organic vapors in Richmond and Hopewell, Virginia and in Staten Island, NY. A methylphenylsilicone column of 1.5 micrometer phase thickness was used with no backflush, and a 10 part per billion mixture of tetrachloroethylene in nitrogen was used as field recalibration standard. Calibrant contamination of the unit was minimal, and background levels of compounds for which the unit was calibrated below 0.5 part per billion could be observed. These compounds were chlorobenzene, ethylbenzene, o-xylene, m-xylene, and bromobenzene. Large releases of benzene, toluene, and several compounds for which the unit had not been calibrated were observed.