A critical literature review of the state of the art for speciation of arsenic, chromium, manganese, and nickel in atmospheric samples was performed. Techniques for distinguishing the compound forms and valence states of these metals were critically assessed. Advantages and limitations of the various speciation approaches were addressed. Three basic types of speciation procedures were identified: (a) direct analysis of particulate matter, (b) speciation of inorganic compounds after dissolution, and (c) sequential or selective extraction. Direct analysis techniques offer the possibility of determining specific compounds but are limited in sensitivity. The latter two techniques cannot determine specific inorganic compounds because of the inclusion of a dissolution step. However, such techniques may give useful information and are more generally applicable than direct analysis techniques. In a few cases (e.g., arsine), compounds may exist in the gas phase and can therefore be readily distinguished from other compound forms of the element.