We propose an automatic test derivation method for testing interoperability of communication protocols. It first derives a skeleton test suite for control part through a sort of reachability analysis. Next, it parameterizes each test case. Finally, it completes the test suite by actualizing test cases by assigning values to their parameters. By constructing test case space based on stable states and by basing test case actualization step on orthogonal arrays used in experimental design techniques, state space explosion is avoided. In order to demonstrate the feasibility and effectiveness, out method is applied to the ATM/B-ISDN signaling protocol and TCP. The application results show that our method surpasses the conventional methods in terms of both test size and coverage. (C) 2003 Elsevier B.V. All rights reserved.