Thieves have stolen 12 canisters of "potentially lethal" laughing gas from a hospital.
The containers of pure nitrous oxide were taken from Ipswich Hospital at 04:40 GMT on Saturday.
The anaesthetic gas "could be harmful and potentially lethal if inhaled or ingested by members of the public", Suffolk Police said.
They are looking for four men who left the area in a dark hatchback car.
The canisters are about 4ft (1.2m) high and are blue with a white stripe around the top.
Nitrous oxide is taken by hundreds of thousands of people every year as a recreational drug, but the gas is also used for pain relief.
It is covered by the Psychoactive Substances Act and is illegal to supply for its psychoactive effect, the Home Office says.