The feasibility of producing a pocket-sized air contaminant monitor based upon a miniature gas chromatograph and an integrated microcomputer has been demonstrated and a practical design for the instrument is presented. This pocket-sized instrument is intended to be used as a personal exposure monitor which is unobtrusively carried by an industrial worker throughout the day. The proposed instrument is fully self-contained in an 8 cm x 4 cm x 15 cm package weighing approximately 0.6 kg. It is build around a miniature integrated gas chromatograph (GC) consisting of a capillary column, a sample injection valve, and detector. A state-of-the-art integrated circuit microcomputer is included in the instrument to handle control and data processing functions. The proposed instrument will be capable of sampling the atmosphere automatically once a minute for eight hours, measuring the concentrations of up to 10 different vapors simultaneously to within 10% accuracy, calculating and storing the time-weighted-average and peak concentrations for each of the gases, measuring concentrations at the 10 ppm level, displaying any of the stored concentrations upon demand, and sounding an alarm when any concentration exceeds a predetermined value. The desirable features of this instrument -- its small size, automatic operation, and ability to monitor multiple gases -- should make it a useful analytical tool and of significant use in the fields of industrial hygiene and occupational safety.