The RSPCA said poisoning was to blame for the deaths of four cats in a Norfolk town.
Two cats belonging to Katharine Snowling in Gorleston had to be put down on 7 November.
They displayed symptoms of poisoning similar to two cats owned by Nadine Fox who lives in a nearby street.
A vet told her the animals had been come into contact with anti-freeze but it is not known if it was accidental or deliberate poisoning.
'Devastated by the loss'
Mrs Snowling said: "The whole family have been devastated by the loss of our cats, and if someone has done this deliberately then this is just awful.
"Our cats suffered tremendously and it was the kindest thing to do to have them put to sleep to ensure they didn't suffer anymore."
RSPCA animal welfare officer Amy Collingsworth said: "We are working with the police to investigate these poisoning incidents and we would urge anyone with any information to contact the RSPCA.
"We would also like to hear from anyone else in the area whose cats may have died from poisoning."
In Norfolk the RSPCA received 12 calls in relation to cat poisoning incidents in 2005 and 18 last year.
The RSPCA said it had teamed up with the Veterinary Poisons Information Service (VPIS) to offer owners detailed information and advice on common poisons.