. If you mean the BASIC code (as text), then try steveastrouk's *.bas. If that doesn't work, RTFM for your interpreter/compiler. . If you mean a text data file, I'd go with *.txt, but it doesn't really matter - you can use whatever you like. If you use *.txt you will be able to double-click on the file and it will open in Notepad (or whatever text editor is set as your default).