Questionnaires are increasingly being used in the workplace to assess exposures to chemicals and other agents. Although the literature contains much information on questionnaire design in general, little information is available on the challenges related to questionnaires applied to the occupational setting. Questionnaires on dry cleaning workers, nurses, farmers, car mechanics, and truck drivers were administered to a total of 25 people currently performing one of these jobs. After asking each question, the interviewer probed to identify the difficulties the respondents had in answering the questions. Overall, the respondents were able to answer the questions. Problems were found, however, with particular questions that reduced the effectiveness of the questionnaire. These included the use of unclear terms, questions open to multiple interpretations, difficult computational requirements (e.g., asking for averages for highly variable tasks), ineffective transitions between topics, and overlapping response categories. This type of testing is a crucial part of questionnaire development and can be used to effectively identify potential problems with questions and, therefore, improve them to enhance collection of higher-quality data for assessments of occupational exposures.