Emergency crews were called to Gotham Court, near Keele Street and Lawrence Avenue West, after the man's wife phoned 911, just after noon.
The 81-year-old was trying to clear a drain and mixed several chemicals together.
He was apparently overcome by the fumes.
Two EMS workers and four firefighters were also exposed to the toxic chemicals and were taken to hospital and later released.
The man's wife was also taken to hospital, but it appears she will be okay.