The authors present ITPG (Interactive Test Pattern Generator), an automatic test pattern generation tool which produces high fault coverage for complex sequential circuits. The tool is more successful than previous attempts at sequential test generation because of the innovative heuristics and high-level sequential primitives used in the system. Old heuristics, such as controllability and observability, have been extended to the sequential world, and a new heuristic, grouping, has been added to accelerate sequential test pattern generation. In addition, the tool allows the designer to influence the test generation process, thus resulting in the 'interactive' nature of the tool. Results from real industrial VLSI circuits show the effectiveness of this tool.