Police have said there is nothing to suggest Novichok caused two people to fall ill at a Prezzo restaurant in Salisbury last night.
A major incident was declared after ambulance crews were called to the restaurant, as emergency services remain on high alert following the poisoning of ex-Russian spy Sergei Skripal and his daughter Yulia in the city in March.
Police last night said: "Earlier this evening, Wiltshire Police and partners declared a major incident following a report that two people had fallen ill in Salisbury.
"Police received a call from the ambulance service to Prezzo restaurant, in High Street, at approximately 6.45pm. Two people, a man aged in his 40s and a woman aged in her 30s, had become unwell.
"Due to recent events in the city and concerns that the pair had been exposed to an unknown substance, a highly precautionary approach was taken by all emergency services.
"Both were taken to Salisbury District Hospital and were clinically assessed. We can now confirm that there is nothing to suggest that Novichok is the substance. Both people remain in hospital under observation."
The major incident has been stood down, but police have said it is not yet clear if any crime has been committed.
A cordon remains in place around restaurant as enquiries continue.