Biomarkers are important in clinical practice because they allow quantitative assessment of diagnosis, disease processes, and treatment response. However, because development of biomarkers lags significantly behind that of drug development, absence of new and appropriate markers may slow the development of patient-tailored targeted therapies. At the 2007 Annual Meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), members of the biomarker committee discussed the possible use of biomarkers in psoriasis and psoriatic arthritis and reviewed the results of several studies of biomarkers in the pathogenesis, diagnosis, and treatment of both the inflammatory and dermatologic aspects of psoriatic disease. We review those discussions.