One of the responsibilities of NIOSH has been the development and evaluation of new sampling and analytical methods for workplace air contaminants. With the recent trend toward lower exposure limit values, there has been a need for reevaluation of existing methods for use at lower concentrations and the development of new sampling and analytical methods. NIOSH began to develop an informal methods manual for its own laboratories, which later became the NIOSH Manual of Analytical Methods. NIOSH also developed a method evaluation protocol to ensure the accuracy of reported exposure data. A key element in this type of research is an experimental evaluation protocol that addresses all the important aspects of the performance of the sampling and analytical method. The authors note that as continued advances are made in sampling and analytical technology, new methods for evaluation will need to be developed as well. An appendix included a summary of key experiments proposed for the revised evaluation protocol for sampling and analytical methods, including analytical recovery, sampler capacity and breakthrough time, sample stability, precision and accuracy.