Chlordane is a toxic, viscous, colorless chlorinated organic chemical that is used as an insecticide and as a fumigant. It has a faint chlorine-like odor. Commercial pesticides that contained it included CD-68, Velsicol, Toxichlor, Niran, Octachlor, Ortho-Chlor, Synchlor, and Corodane.
From 1948 to 1978, the chemical was widely used in the United States as a pesticide and fumigant on crops and ornamental plants. In 1983, the EPA restricted the use of this chemical to below-ground termite control around houses. In 1988, however, the EPA entirely banned the use of the chemical in the U.S.. The vapors of the chemical are often detectable in many older homes, particularly in basements and crawl spaces. It is still manufactured in the U.S. for export, unfortunately.
Symptoms of poisoning include a wide range of digestive and central nervous system problems like headaches, nausea, convulsions and severe depression; there is no antidote. The body tends to store the chemical in one's fat. Chronic exposure can cause liver and nerve damage and possibly cancer.
Based on work I did for the science dictionary at http://biotech.icmb.utexas.edu/ and augmented with research from http://www.atsdr.cdc.gov/ToxProfiles/phs8906.html