"Kalaignar (Karunanidhi), who had received treatment (at home) for the allergy and was taking rest, has been admitted to Kauvery Hospital to undergo further tests and related treatments," the DMK said in a release.
The hospital said Karunanidhi was "admitted for optimisation of nutrition and hydration" and was being treated by a team of doctors.
"He is stable and being treated by a team of doctors. He will be in the hospital for a few days," Kauvery Hospital Executive Director Aravindan Selvaraj said in a release.
On October 25, DMK had announced that Karunanidhi was suffering from allergy "caused by a medicine he has been using" and advised rest by doctors.
The leader, who is seen regularly in the public, has since confined himself to his home, although he had been issuing statements and reacting on key matters such as demonetisation.
He had also skipped campaigning in the elections to three Tamil Nadu Assembly seats last month. Ruling AIADMK won all three constituencies.