We introduce a new type of test, called exclusive test, und discuss its application to fault diagnosis in combinational circuits. A test that detects exactly one fault from a given pair of faults is called an exclusive test. In general, generation of an exclusive test by a conventional automatic test generator requires a model of the circuit with multiple-faults. We describe an ATPG model that transforms the exclusive test problem into a single-fault test generation problem. We present a generalized diagnostic method and illustrate the use of exclusive tests in improving the diagnostic resolution of a test set. Results of diagnosis with exclusive tests for ISCAS85 bencmark circuits are included.