The pets both fell sick after eating dog treats thought to have been deliberately left on a street in Leeming, near Northallerton.
Vets have now confirmed that the animals had ingested a toxic substance, and further blood tests are being carried out.
The first report came on April 10 and the second the following afternoon in the St John's Road area.
In both cases, the owners described their dogs becoming very ill with symptoms including panting, struggling to walk, vomiting, diarrhoea and burning in the mouth and throat.
One of the dogs is in a serious condition.
North Yorkshire Police have examined the scene and carried out house-to-house enquiries as part of the ongoing investigation.
Concerned residents are due to raise the matter with parish councillors. It has already been brought to the attention of Hambleton District Council’s environmental health and dog warden teams.
To help the investigation, police are urging people to come forward with information about these incidents and to report any suspicious behaviour in the St John’s Road area in recent weeks.
Although the force have not confirmed that the biscuits were the source of the poisoning, posts on a community Facebook page for Bedale residents claimed that the treats had been laced with the substance.
Contact North Yorkshire Police on 101, select option 2, and ask for Paul Enbom, or email [email protected] Quote reference number 12180061854 when providing details about the case.