Twenty-five people are in hospital in Germany after eating bread rolls laced with rat poison, which were left at their firm as "a gift", police say.
The workers at a plastics company in Lower Saxony helped themselves to the food, left in a box with a note.
Tests carried out on the bread overnight at a Berlin laboratory confirmed the presence of rat poison.
Police said the 25 were under observation but so far no-one had shown symptoms of poisoning.
"We don't believe the amount of poison used would have been deadly, but it could have caused serious illness," police spokesman Frank Soika was quoted by the Associated Press as saying.
The victims are being monitored as medical staff were unsure how long it would take for the poison to work, according to local media.
The employees had begun eating the rolls when someone noticed an unusual substance on them and called the emergency services.
The leftover rolls were flown by helicopter to a specialist laboratory in Berlin for testing.
The identity of the perpetrator and the motive remain unclear.