Methodology was developed to determine unambiguously trace levels of volatile organic compounds as they vary in concentration over a variety of time scales. This capability is important because volatile organic compounds (VOCs) are usually measured by time-integrative techniques that average peak exposures to insignificance. The specific method involves a preprogrammed sequential syringe sampler that can fill 150-cu cm syringes with air at rates of 2 to 90 min per syringe. The 12 collected samples are then transported to the laboratory for fully automated gas-chromatographic separation with mass spectrometric detection. The instrumentation and method are described, and representative results are given to document the variability in VOC concentrations in situations such as use of household products and water outgassing in residential air, automobiles during driving, and office indoor air that is subject to ventilation system cycling. The method is shown to perform automatically in both sampling and analytical modes. Contamination and sample integrity tests show typical precision to be about 10% relative standard deviation. Field tests show that VOC concentrations can vary by greater than an order of magnitude on different time scales. (Copyright (c) 1989 Gordon and Breach, Science Publishers.)