Police in Harrow were called to Bacon Lane, Edgware at 13:30hrs on Sunday, 8 April following reports of a two unresponsive males in a residential address.
Officers, London Ambulance Service and London Fire Brigade attended. Two men believed to be aged 38 and 42-years-old were found deceased at the address.
These deaths are being treated as unexplained. A post-mortem examination will be held in due course.
At this early stage, police believe that there was a possible carbon monoxide leak at the address.
Five other people residing at the property, which is a multiple occupancy address, have been taken to hospital as a precautionary measure.
A neighbouring property was evacuated as a precaution but the residents have since been allowed to return.
No arrests have been made.
Police in Harrow continue to deal alongside the Health and Safety Executive who has been informed.