Prior to the late 1970's, a lot of drywall compound (sometimes called mud, and used for filling corners and seams) was made using asbestos. The reason? Fire resistance -- it could keep a fire from spreading. But the workers were getting sick - and dying - from a special kind of cancer. Asbestos is no longer allowed in any building materials.
You have to think twice before ripping walls open that were drywalled before about 1980. If you're buying a house that will need a lot of renovations and maybe require new walls, remember that you should have tests done on your walls to determine if there is asbestos in the compound. There are specialists who will come to your house and do this, or you can scrape off small samples and send them to a testing lab. Asbestos is not harmful if it's left in place. But when you disturb it, you will send those dangerous fibers into the air. Don't take the risk.
