Poor adherence to recommended regimens is a substantial problem in the clinical management of adults with asthma and other chronic diseases. Research on adherence assessment is complicated by methodological difficulties including limitations associated with the use of self-report measures. In this study, psychometric techniques were used to analyze two self-report scales for assessing adherence to recommended medication and inhaler use regimens in adults with asthma. Results indicated that the two scales had standard deviations large enough to detect variation adherence, had adequate reliability, and reflected the impact of an intervention designed to improve adherence. The results supported the usefulness of these scales for research on adherence. Additional analyses indicated that the two scales could be combined if the research goal required an overall measure of adherence.