The protocol for evaluation of sampling and analytical methods for airborne contaminants originally developed in 1974 for NIOSH and OSHA was expanded; these guidelines provided the expanded protocol. Procedures to follow in estimating the precision, bias and accuracy of a sampling and analytical method were presented. Guidance and procedures to evaluate a method relative to the 25% accuracy criterion in terms of one of three mutually exclusive possible conclusions (positive, negative, or inconclusive) were included. The procedure was made up of five steps: selection of compounds for method development and evaluation; development of the sampling and analytical method; evaluation of the method; preparation of a written version of the method; and preparation of a technical report on the development and evaluation. The method evaluation section discussed recovery of the analyte from the medium, stability of analyte on the sampling medium, stability of the sampling medium prior to use, sample generation, capacity of the sampler and the sampling rate, pressure drop across the sampler, precision, bias, and accuracy, and field evaluation.