In this language treatment experiment we compared a stimulation technique and a linguistically oriented learning approach for the use of interrogative words and prepositions. These function words had to be used in a short dialogue text comprising a wh-question with an interrogative word and an elliptic answer with a temporal prepositional phrase. The text was embedded in a short description of the situational context. Twelve chronic aphasic patients took part in this two-period cross-over treatment experiment-nine had Broca's aphasia, three Wernicke's aphasia. They had a medium overall level of aphasic impairment as measured by the Aachen Aphasia Test. Nonparametric tests yielded significantly larger direct effects for the linguistically oriented learning approach (L), but significantly larger after-effects for the stimulation approach (S). Thus, the S/L sequence was more efficacious. Transfer effects to non-trained spatial function words were also present, but to a lesser degree. Methods from criterion-referenced measurement were used to assess treatment effects, both improvement and mastery, in individual patients. Aphasics with additional speech apraxia showed deviations from the overall improvement pattern.