Abstract
The ideal analytical method is one which has been thoroughly evaluated, collaboratively tested by a number of laboratories, and established by long usage. The development of such procedures is time consuming and expensive. However, a classification scheme which recognizes that methods may be used which have not been fully evaluated or collaboratively tested is useful. A scheme with five classes which has been applied to NIOSH analytical methods is presented. It recognizes that many analytical methods have been developed, that other agencies and organizations have examined the literature and published methods, and that unproved or suggested method may be the only information available.