Hi Bill: To sterilize your glass petri dishes, bake the clean DRY dishes in your oven at 500 degrees for 40 minutes. No foolin'. That's what we do routinely. It helps if you have something to put them in, like a metal box, but if you are careful, it is not necessary. Keith Klein Dept. of Biol. Sci. Mankato State University Mankato, MN 56002