An overview of the methodological aspects of performing inhalation studies was presented. Special critical factors considered included the design and operation of exposure chambers, control of the experimental atmospheres, and operational health and safety. The design and operation of a dynamic exposure chamber were described. Systems ranging from simple chambers to highly automated chambers were reviewed. Characteristics of experimental atmospheres, ranging from those for a single test material to those for complex mixtures, were considered emphasizing generation of a constant and known concentration of material and existence of analytical control of the atmospheric concentrations. The importance of the health and safety of the personnel directly involved in the conduct of the study was emphasized. Requirements for safety equipment, periodic physical examination, and other safety and health procedures were discussed. Continuous and intermittent maintenance of experimental animals was described. Experimental design for determining long term low level exposure risks, multilevel exposure, and accidental exposure risks was discussed. Assessment of biologic effects and quality control were considered.