This article is a critical review of some of the methods that have been used for the sampling, analysis, and monitoring of vapor-phase toluene diisocyanate (TDI). Only some of the methods that have received relatively widespread application have been addressed in this article. This review includes a "tutorial style" discussion of basic definitions and basic principles and procedures of quality control and metrology for sampling, analysis, and monitoring. One critical issue that is addressed: Are there methods and monitoring instruments available that are capable of sampling and analyzing or monitoring TDI vapor with sufficient speed and sensitivity to satisfy the requirements of the current ACGIH[sup ®] threshold limit values (TLVs[sup ®]) for TDI vapor? [ABSTRACT FROM AUTHOR]