Eight men have been arrested after police uncovered a large-scale drug operation being run out of homes in Melbourne's north and west.

Detectives found more than 3000 cannabis plants and hydroponic set-ups in houses in Mill Park, Epping, Wollert and South Morang.

A 52-year-old Greenvale man and a 52-year-old Lalor man have been charged with cultivating and trafficking a large commercial quantity of drugs.

An Epping man, 52, has been charged with a number of counts of relating to the cultivation of a commercial quantity of drugs.

A further five men from Melbourne's west face counts of cultivating and trafficking a commercial quantity of drugs.

A 36-year-old Thomastown man has been released pending further inquiries.