Those at highest risk for being victims of poisoning are the terminally ill and mentally incapacitated, drug addicts, the elderly, and the very young. Unwanted spouses or lovers compose another high-risk group. The offender is usually personally involved with the victim and is often a caregiver. Poisoners often assume the role of attempting to "nurse" the victim back to health. Poisoners often derive pleasure from seeing their victims suffer, and serial poisoners usually enjoy the thrill of having power over the life and suffering of the victim. Perpetrators of homicidal poisonings are often employed in the medical or caregiving fields. Substances that can be lethal in small amounts appeal most to perpetrators. The ideal poison for a homicide is odorless, tasteless, difficult to detect, and a bearer of symptoms similar to naturally occurring diseases. It has become increasingly difficult to find a poison with all of these features, since modern scientific methods and advances have made it easier to detect poisons. This article profiles the following poisons that have been used to perpetrate homicidal poisoning: arsenic, cyanide, thallium, strychnine, aconitine, atropine, and antimony. Some "red flags" that indicate homicidal poisoning are sudden death; the association of a caregiver with other illnesses or deaths; whether the victim received medical treatment, appeared to recover, and then died later; caregiver access to restricted drugs or other chemicals; and caregiver isolation of the victim. The forensic toxicologist narrows the list of poisons that may have been used. This article describes the stages in which this is done.