This manual provided information on sampling and analytical methods for monitoring occupational exposures to toxic substances in air and biological samples. The monitoring methods discussed in this edition included those for the collection of aerosols, gases, and vapors in air with active samplers such as filters, sorbent tubes and impingers, and laboratory analysis. Also considered were diffusion samplers and direct reading field instruments. For each method, information was provided on sampling and measurement parameters, limit of detection, working range, precision, and interferences. An accuracy estimate was provided for each method discussed. Reagents and equipment were listed, along with special precautions, instructions for sampling, sample preparation, calibration and quality control, measurement, and calculations. Discussions of specific topics of general interest were also included, such as method development and evaluation, and discussions of some portable direct reading instrumentation.