The purpose of this study was to evaluate the serum levels of hyaluronic acid (HA) in a group of patients with psoriatic arthritis (PsA), with special emphasis on the relationships between HA levels and clinical parameters of joint and skin activity. Thirty-four patients with PsA, 34 patients with rheumatoid arthritis (RA) and 49 healthy volunteers participated in the study. Assessment of joint disease in patients with PsA included duration of morning stiffness, number of tender and swollen joints, right and left grip, the presence of inflammatory back pain and Schober's test. The current severity of skin involvement was graded according to the Psoriasis Area Severity Index (PASI). Serum levels of HA were measured by a radiometric assay. The mean HA serum levels of patients with PsA and RA were significantly increased in comparison with healthy controls (107 +/- 39.6 microg/dl in patients with PsA, whereas in patients with RA it was 168 +/- 32.4 microg/dl and 36.7 +/- 5.5 microg/dl in healthy controls). A highly significant correlation was found between levels of HA and index of skin involvement, but no association was found between HA levels and clinical parameters of joint severity. We conclude that in this cohort of patients with PsA, HA levels clearly reflected psoriatic skin involvement although it did not correlate with joint disease.