Portable gas chromatography (PGC) as utilized in the fields of environmental chemistry and industrial hygiene is an adaptation of one of the most frequently utilized techniques in organic chemistry analysis. To produce instruments which are "portable," the manufacturers of the instruments described below have reduced both the size and weight of the analytical equipment, yet at the same time included options such as internal batteries and cylinders for carrier gas not necessary for laboratory instruments. In a discussion on portable analytical instruments in general, Newman wrote: "Like the personal computer, succeeding generations of analytical instruments have shrunk in size and weight even as they have become more sophisticated and versatile." In addition to PGC, Newman's paper on portable instruments discussed other analytical techniques including mass spectrometry, X-ray fluorescence, and infrared spectrometry, and he included as "portable" units up to a hundred pounds. Portable GCs discussed in the current article are we 11 under half that weight, and have been developed from the base up as innovative designs rather than shrunken versions of existing instrumentation. For the purposes of this article, a PGC w ill be one which weighs less than approximately 50 pounds (20 kg), and is capable of operating independently of external power. PCGs currently available on the commercial market are a compromise between an instrument easily used in the field and an instrument with full laboratory capabilities. Limitations of PGCs will be discussed below, but it should be understood by the reader that it is not the intention of these instruments to replace the lab unit in all of its capabilities. For example, portable instruments must compromise between the need for power required to achieve high temperatures (greater than approximately 1 00 degrees-C) or temperature programming, and the need to minimize weight by limiting battery size. One concession universal to the instruments discussed in this review is that they all accept injection of a gaseous sample, while most lab instruments will readily accept a liquid sample injected into a heated injector for vaporization. Certain concessions also have been made in instrument specificity and sensitivity. There seems to be a tendency, as will be noted in the citations below, to discuss these instruments in terms of "field screening methods" or other qualifiers. Although there certainly are those who would disagree, particularly among the manufacturers of the instruments which tout their PGCs capability to "identify" unknown compounds and quantify extremely low levels of analytes, it is the opinion of these authors that the better PGCs, in general, lack the capabilities of the better lab-grade instruments. They do, however, perform certain functions which their lab counterparts cannot.