Serum copper, iron and ceruloplasmin concentrations were determined in 45 subjects (22 males and 23 females, medium age 50.3, range 25-76) diagnosed as psoriatic arthritic patients (20 with poliarticular, 12 with mono-oligoarticular and 13 with spondyloarticular form), in 63 patients (30 males and 33 females, medium age 32.4, range 10-78) with psoriasis, and in 60 blood donors (32 women and 28 men) as reference group. Mean serum copper, iron and ceruloplasmin was significantly increased (p less than .001) in psoriatic arthritis as compared with controls or subjects with psoriasis alone. The number of synovial joints affected was significantly correlated to changes in these serum parameters. Indeed, serum copper, iron and ceruloplasmin were found to be significantly different from that of normals in the polyarticular subgroup (p less than .001), while only copper and ceruloplasmin were different in the mono-oligoarticular form (p less than .001 and p less than .01 respectively). No significant changes were found in a spondyloarticular subgroup. In the polyarticular subgroup a direct correlation was found between another disease activity marker (e.g. ESR) and serum changes in iron, ceruloplasmin and copper (p less than .001). Our data indicate that psoriatic arthritis is a multifaceted disease: the polyarticular form behaves like seronegative rheumatoid arthritis, while the monoarticular forms shows a lesser involvement of serum iron; spondylitic arthritis does not show any significant change in serum copper, ceruloplasmin and iron concentrations.