Biomarkers in psoriatic arthritis (PsA) may serve as surrogate end points for disease outcome and can provide insights into disease susceptibility and natural history. Biomarkers could relate to diagnosis, pathogenesis, prognosis, therapeutic response, and comorbidities. The "felt need" is, however, in the development of biomarkers for the presence of PsA in patients with psoriasis, as well as that for joint damage. During the past few years, many studies related to PsA biomarkers have been conducted. These studies are reviewed here. C-reactive protein, matrix metalloproteinase-3, and circulating osteoclast precursors show promise. An international goal-directed study to determine biomarkers for joint damage in PsA is now under way through a collaborative effort of GRAPPA (the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis) and OMERACT (Outcome Measures for Rheumatology Clinical Trials).