Police have released CCTV images after up to 15 syringes of dangerous medication were stolen from a hospital in south London.
Detectives fear the drugs may be harmful if wrongly administered and could trigger a potentially fatal allergic reaction.
A man and a boy allegedly walked into Purley and District War Memorial Hospital and stole the syringes of anti-tetanus drug Revaxis at about 5pm on Wednesday.
They left the facility by 5.15pm, police said.
A Scotland Yard spokesman said: "The drugs can be harmful if administered incorrectly and could cause an allergic reaction leading to anaphylaxis, which in turn can cause extreme breathing difficulties.
"Detectives are keen to trace those responsible and ensure the safe return of the drugs."
The man was described as white, aged between 20 and 30, and wearing a red top, a cream coloured jacket, grey jogging trousers and white trainers.
The boy was white with dark har, about 10 to14 years old, and wore a grey T-shirt, red shorts, white socks and black trainers.
Police released two CCTV stills of a man they want to speak to.
Anyone with any information should call police on 101 quoting reference CRIS 3829296/15 or contact Crimestoppers to remain anonymous on 0800 555 111.
