Phosphine is an extremely toxic gas generally seen in the farming industry, in which it is used as a grain fumigant. It can also be generated as a by-product during the manufacture of methamphetamine. This article describes how the gas is formed, reviews the toxicity, health effects and symptoms of exposure, addresses the safety concerns regarding potential exposure to law enforcement personnel, and describes protective equipment available for personnel who respond to incidents in clandestine laboratories. The article relates an incident in which sheriff’s deputies, who were not wearing protective clothing or masks, investigated the death of three individuals suspected to have been overcome by phosphine gas. In addition to the hazard of the phosphine gas, the oxygen-deficient atmosphere and the lower explosive limits of solvents present were also of concern. The article recommends increased awareness and communication between criminalists and sworn field personnel, practical training for narcotics officers, patrol officers, and other first responders in conducting investigations of clandestine laboratories, and use of safety equipment by responding personnel. Figures, references