A method for metering nutrient media into a plurality of cell culture bags in substantially aseptic manner, which method comprises passing liquid nutrient media through a media flow conduit which is in substantially aseptic connection at one end with a source of said media, and metering aliquots of said media through a downstream portion of said media flow conduit through a plurality of branching conduit end portions, into a plurality of flat, flexible bags which are separately attached to individual conduit end portions in substantially aseptic manner, and sequentially filling said flat bags with a predetermined-volume aliquot of media, at least part of which bags are made of a material capable of providing at least two times the oxygen diffusion and at least two times the carbon dioxide diffusion between the bag interior and exterior, compared with an identically sized, sealed bag having a polyethylene wall 0.013 inch thick, including the step of sequentially and repeatedly passing aliquots of predetermined volume through said downstream, branched portion of said flow conduit sequentially into each of said plurality of flexible bags, whereby said plurality of bags may be filled with said predetermined-volume aliquots of media in substantially aseptic manner, and culturing human white blood cells in the nutrient media within said flexible bags.