An ignition system for internal combustion engines includes a monitoring circuit (9) which is used for introducing appropriate emergency measures for protecting the catalyst in the case of faulty ignitions. The ignition system includes an evaluation device (10), which subjects the ignition-diagnostic signal (Zund OK) to statistical weighting and, when the weighted ignition-diagnostic value (ZUNTAB) exceeds a specified threshold, introduces appropriate measures, the evaluation being continued steadily so that if the value subsequently falls below the fault threshold (AFSDZU), correction is recognized and the emergency measures are withdrawn.