MCAID is a relatively machine-independent technique for writing computer-aided instructional material consisting of descriptive text, multiple choice questions, and the ability to call compiled subroutines to perform extensive calculations. It was specially developed to incorporate test-authoring around complex mathematical models to explore a specific subject area, thus combining two broad categories of computer assisted instruction (CAI): programmed text and simulation programs. The text material and the associated branching information are contained on the text-file; computational routines reside in the compiled library. The MCAID driver, which monitors overall control, is programmed in FORTRAN and can be adapted to other programming languages. The driver, however, relies heavily on the ability to perform random access read/write on a card-image disc file, which contains all the test material and the branched logic. The driver has been successfully used at McMaster University to develop teaching and evaluation programs around complex physiological models. It has also been used to adapt CAI material developed elsewhere to a mini-computer. A simplified flow chart of the driver and examples of a typical test file and a typical student dialogue are appended. (Author/VT)