In the broadest sense, toxicology is the science involving the study of poisons. It is concerned with the physical properties of toxic substances, their effects upon the body, their identification, and the treatment of poisonings. Poisonings may be suicidal, accidental, or homicidal, with the majority of cases falling into the first two categories. Proof of poisoning is based upon several factors, taken singly or in combination, including evidence of signs and symptoms associated with a specific toxic substance, demonstration by chemical analysis of the presence of food or drug taken by the deceased or presence of substances in body taken by the deceased or presence of substances in body tissues and fluids, gross or histologic pathological fiindings, or a history of exposure of the deceased to a specific toxic substance. Analysis of gastric contents is insufficient to prove poisoning, because many poisons are rapidly absorbed into the system. Proof rests only with demonstration of absorption of the toxic substance. A pathologist who performs a medicolegal autopsy has the primary responsibility for the collection and preservation of toxicologic samples. It is suggested that the following samples be retained for analysis: heart blood sample, urine sample, gastric contents, duodenal contents, bile, kidney, half of the liver, half of the brain, a sample of body fat, one lung, and samples of bone and hair. Each sample should be placed in a separate container, properly sealed and labeled. In the majority of cases that involve poisoning as a cause of death, a specific substance is suspected, and a direct analysis for the substance can be made. Autopsy on an unembalmed body yields more accurate results. Cyanide, for example, reacts chemically with embalming fluids and becomes unidentifiable. The five major groups of toxic substances are noxious gases, steam volatile substances, metallic poisons, nonvolatile organic poisons, and miscellaneous substances. Toxicologists are often required to give court testimony. Seven references, a photograph, and a table are included. For related documents, see NCJ 69731-42 and 69744-47.