Formaldehyde is a substance hazardous to health, specified in Schedule 1 to the British Control of Substances Hazardous to Health Regulations 1988 but still used in laboratories as a preservative and for disinfection of surfaces and spaces. In this paper we review the properties and hazards of formaldehyde and its common laboratory uses, and suggest some precautions and ways of minimising risk from those fumigation procedures that carry the greatest risk of exposure to high levels of the gas.