Although the efficacy of isoniazid in the prevention of tuberculosis in HIV-infected persons with a positive tuberculin skin test is proven, several feasibility issues remain unanswered. In resource poor settings where a chest radiograph may not be readily available, the question of whether cough alone is an adequate screening tool needs to be considered. We analysed screening data collected as part of an isoniazid efficacy study. Although the study was not designed specifically to answer this question, the data suggests that cough alone may be inadequate for screening patients for potential tuberculosis preventive therapy, and that a chest radiograph may be necessary. Feasibility studies are needed.