38-year-old Sugan and his sons Sarvan (17) and Surendra (14) were found dead in their house this morning, Joint Commissioner of Police Sidhhraj Bhati said.
A 90-year-old neighbour Samtaben was also taken ill after being exposed to the gas and is hospitalised, he said.
Narol is a hub of textile processing units and police are also probing if the contaminated effluents from the factories were dumped into drainage pipes.
Forensic Science Laboratory personnel have taken samples from the drainage line.
