A method for online testing pipeline systems comprising a succession of stages separated by buffers each associated with an idle signal, or idle signal, and/or at least one status bit, comprising: detecting values of the idle signal and/or the corresponding status bits indicating the availability of a cycle or the abrupt interruption of the flow of operations in a pipeline, and indicating that a valid operation, executed by a stage in the pipeline, is followed by an unused cycle; maintaining the state of the buffer in order to allow said valid operation to be re-executed during the unused cycle indicated by said idle signal; re-executing, during the unused cycle, the valid operation, in order to obtain at least a first version and a second version of said valid operation; memorizing, at the output of the pipeline, the results that correspond to the first version of said repeated or re-executed operation, in order to compare with the results of said second version of the same repeated or re-executed operation; and comparing the results obtained at the output of the pipeline, which results correspond to the first version and the second version, and, if there is a difference, indicating an error.