Many commericially available computer programs contain test-type materials, and some courseware makes use of testing techniques as an instructional device. The area in which testing techniques are used most effectively for teaching is self-instruction. Most microcomputers operate using the BASIC language, but authoring languages are the most easily used by teachers. EXTOL, an authoring aid developed at the University of Essex (England) specifically for language teaching, has powerful testing capabilities. EXTOL uses a driver program written in PASCAL or FORTRAN, contains only 17 commands, has been used to develop multiple-choice and cloze tests, and can report the current score of correct answers to the student. The unique qualities of computers can be of use in testing in a variety of other ways, including investigating the relationship of lexical availability and cloze test performance, speed of response, speed of comprehension, and availability of structures for productive purposes. The EXTOL commands are appended. (MSE)