The Outer Limits 1995 s1 e 5 The Second Soul

When an alien race makes first contact with the Earth, they request only one thing: Earth's dead. It seems the alien beings exist in a gaseous state that will come to an end if they are not given host bodies to occupy. The bodies of the dead will serve that function. One year later, Dr. Michael Alders is in charge of the program to provide the aliens with bodies. He considers them them to be parasites but carries on as best he can. When his best friends, Karen and James Heatherton die and are included in the program, his discomfort grows. When he learns however that the aliens have transported potentially toxic gases to Earth, he assumes the worse.