As long as a labeled training set is available, string kernels can reach state-of-the-art results in various languages including English [7,<cite> 13,</cite> 23] , Arabic [4, 17, 18, 24] , Chinese [35] and Norwegian [24] . Different from all these recent approaches, we use unlabeled data from the test set in a transductive setting in order to significantly increase the performance of string kernels.