A questionnaire used in student evaluations of interdisciplinary courses during six semesters contained two Likert items stated in a direct negative mode which were embedded in a questionnaire (14-18 items) in which the remaining items were phrased in a direct positive mode. In the seventh semester and thereafter, the two negative items were restated as direct positive stems. Item-analysis demonstrated that in the direct negative mode, the two items had low item-to-total correlations and that the internal consistency reliability of the sum score could be improved by eliminating the two negatively phrased items. Also, the two negatively worded items defined a separate factor. After they were reworded into a direct positive mode, these two items showed markedly improved item-to-total correlations. Moreover, the unique factor disappeared, which suggests that it was a methodological artefact probably attributable to respondent carelessness. Including a few negative items in an otherwise positively stated questionnaire leads to ambiguity of results rather than controlling for response sets. We therefore recommend against the practice. (Contains 4 tables.)