MetaPrime: An interactive fault-tree analyzer. The performances of almost all available fault tree analysis tools are limited by the performance of their prime implicant computation procedure. All these procedures manipulate the prime implicants of the fault trees in extension, so that the analysis costs are directly related to the number of prime implicants to be generated, which in practice makes these tools difficult to apply on fault trees with more than 20 000 prime implicants. This paper introduces an analysis method of coherent as well as noncoherent fault trees that overcomes this limitation because its computational cost is related to neither the number of basic events, nor the number of gates, nor the number of prime implicants of these trees. The authors present the concepts underlying the prototype tool MetaPrime, and the experimental results obtained with this tool on real fault trees. These results show that these concepts provide complete analysis in seconds on fault trees that no previously available technique could ever even partially analyze, for instance noncoherent fault trees with more than 1020 prime implicants. These concepts can also be used to analyze event trees because such trees denote Boolean functions on which these concepts can be applied. Prime implicant computation is also critical in many other domains, in particular in expert system applications such as reasoning maintenance and multiple fault diagnosis. The application of the concepts underlying MetaPrime to the resolution of these problems is under study.