A machine for automatically filling plastic bags with liquid or particulate material moves a continuous web of such bags through a number of serially positioned work stations. The bags are completely sealed when they enter the machine. As each bag passes through a slitting work station, a specially shaped opening is cut into the bag near an end of it which will become its top. When the bag proceeds to a filling work station, it is held vertically and a specially shaped fill nozzle is moved downward and rotated for entry into the bag through the slit opening. A valve is provided within the fill nozzle for controlling entry of the material into the bag. The valve and fill nozzle are cooperatively controlled by a single mechanism. The bags are transported through the various work stations by a positive toothed belt drive that preferably holds the bags flat until the filling station, wherein the belts are then moveable toward and away from each other in order to allow filling of the bag. After filling, the bag opening is then sealed. The various techniques are especially useful for aseptic packaging of foods, such as milk and wine. Fitments for later use in removing material can also be added to the bag in another work station. The bags and fitments are structured and carried in a way to cooperate with the machine.