Chemical hypersensitivity syndrome (CHS) is a chronic, multi-system disorder, usually involving symptoms of the central nervous system and at least one other system. Environmental concentrations of natural chemicals such as ozone and oxides of nitrogen are many orders of magnitude higher than in the past. Chemical hypersensitivity syndrome is an acquired disorder characterized by recurrent symptoms, referable to multiple organ systems, occurring in response to demonstrable exposure to many chemically unrelated compounds at doses far those established in the general population to cause harmful effects. Diagnosis of the victims with CHS is usually possible, by a combination of a detailed history, physical examination, and a few specific biochemical tests. The concept of chemical hypersensitivity as a disease entity in which the individual experiences numerous symptoms from numerous chemicals caused by a disturbance of the immune systems lacks a scientific foundation.